BYETOOLS HYPERTECHWORK

SISTEM ENJIN DUA LEJANG

2011-10-31T14:01:00.007+08:00

Enjin dua lejang mempunyai prinsip pengendalian yang berbeza daripada enjin empat lejang iaitu enjin dua lejang melengkapkan keempat-empat proses (masukan, mampatan, kuasa dan ekzos) yang dilakukan pada enjin empat lejang dalam setiap dua lejang, ataupun setiap satu putaran enjin sahaja. Ia dilakukan dengan menggunakan bahagian permulaan lejang mampatan bagi melaksanakan fungsi lejang masukan dan ekzos secara serentak. Dengan ini, enjin dua lejang menghasilkan kuasa spesifik yang lebih tinggi, menjadikannya sesuai bagi kerja-kerja ringan dan mudah alih seperti gergaji rantai sehinggalah kepada penggunaan berskala besar seperti lokomotif kereta api.

Dari segi pelinciran, enjin petrol dua lejang memerlukan minyak pelincir khas yang boleh terbakar, dikenali sebagai minyak 2T disebabkan operasi kitar dua lejang turut melibatkan ruangan dalam kotak engkol, tidak seperti kotak engkol enjin empat lejang yang terasing sepenuhnya daripada kebuk pembakaran. Pembakaran minyak 2T ini merupakan satu penyebab utama kepada pencemaran yang dihasilkan oleh enjin petrol dua lejang..

Penciptaan kitar dua lejang mula dilakukan oleh Dugald Clark sekitar 1880 dengan enjin yang mempunyai silinder pengepam berasingan. Enjin pengepaman kotak engkol, yang menggunakan kotak engkol sebagai pengepam, telah dicipta oleh Joseph Day (dan Frederick Cock bagi liang masukan kawalan omboh).

Enjin dua lejang, dengan paip ekzos pengembangan menunjukkan kesan pantulan gelombang tekanan. Ciri ini didapati dalam reka bentuk enjin berprestasi tertinggi.
Isi kandungan

Kitar dua lejang

Enjin dua lejang beroperasi dengan hanya dua lejang, berbanding empat lejang bagi enjin kitar Otto:

Kuasa/ekzos - Peringkat ini bermula sebaik sahaja campuran udara-bahan api terbakar, menyebabkan gas pengembangan mengembang dan memaksa omboh turun ke bawah, menghasilkan kuasa pada enjin. Gerakan omboh ke bawah juga memampatkan campuran udara-bahan api-pelincir, maka apabila omboh terus bergerak ke bawah sehingga membuka liang masukan dan liang ekzos, gerakan omboh ke bawah memaksa campuran udara-bahan api-pelincir yang segar masuk ke dalam kebuk pembakaran dan memaksa gas ekzos keluar.

Masukan/mampatan - Omboh bergerak ke atas dan memampatkan campuran udara-bahan api-pelincir. Gerakan omboh ke atas menyebabkan tekanan udara di dalam kotak engkol menjadi rendah, membolehkan campuran udara-bahan api-pelincir dari karburetor masuk ke dalam kotak engkol melalui satu injap dedaun. Campuran udara-bahan api-pelincir termampat dibakar, dan kitar dua lejang berulang.

Kebaikan dan kelemahan enjin dua lejang

Enjin dua lejang adalah ringkas, maka kos membaik pulih enjin dua lejang adalah lebih murah berbanding enjin empat lejang. Selain itu, prinsip pengendalian enjin dua lejang juga menjadikannya sesuai bagi penggunaan yang memerlukan enjin yang mudah alih dan ringan seperti gergaji rantai dan mesin rumput. Enjin dua lejang juga boleh menghasilkan kuasa hampir dua kali ganda saiz enjin empat lejang yang sama, misalnya motosikal Honda CBR 150 4 lejang hanya menghasilkan kuasa sebanyak 18.98 bhp tetapi motosikal Honda NSR 150 2 lejang pula menghasilkan kuasa sebanyak 38 bhp.

Sungguhpun demikian, penggunaan enjin dua lejang semakin berkurangan disebabkan keluaran gas ekzos enjin dua lejang yang kurang mesra alam berbanding enjin empat lejang. Faktor-faktor utama yang menyebabkan penghasilan gas-gas ekzos yang mencemar udara oleh enjin dua lejang ialah pembakaran minyak 2T serta proses ekzos yang menyebabkan sebahagian campuran udara-bahan api-pelincir yang tak terbakar turut disingkirkan, mengurangkan kecekapan enjin.

Langkah-langkah yang diambil bagi meningkatkan kecekapan enjin dua lejang adalah seperti berikut:-

Injap kuasa dua lejang - Injap kuasa melaras saiz bukaan liang ekzos bagi kuasa yang optimum serta meningkatkan kecekapan enjin. Pada putaran enjin rendah, injap kuasa mengecilkan bukaan ling ekzos bagi mengelakkan pembaziran bahan api dan pelincir serta meningkatkan kilasan peringkat bawahan. Pada putaran enjin tinggi pula, injap kuasa membesarkan bukaan liang ekzos untuk penyingkiran gas ekzos yang lebih lawas, meningkatkan kuasa enjin.

Kebuk pengembangan - Kebuk pengembangan adalah ruangan pada paip ekzos enjin 2 lejang yang membonjol. Fungsinya adalah untuk meningkatkan kecekapan enjin melalui balikan gelombang tekanan gas ekzos.

Suntikan terus - Di dalam sesetengah enjin petrol dua lejang, minyak petrol disuntik secara terus ke dalam kebuk pembakaran manakala minyak enjin dua lejang disuntuk secara terus ke bahagian bergerak di dalam enjin seperti galas aci engkol. Melalui suntikan terus, penghasilan gas ekzos tercemar disebabkan pembakaran minyak enjin dua lejang dapat dikurangkan.

Penukar bermangkin - Penukar bermangkin dipasang bagi mengurangkan penghasilan gas-gas toksik yang mencemarkan udara di dalam gas ekzos.

Enjin diesel dua lejang

Enjin diesel dua lejang mempunyai reka bentuk yang berbeza daripada enjin petrol dua lejang. Di dalam enjin diesel dua lejang, udara masuk melalui liang masukan di bahagian tepi silinder dan tidak melalui kotak engkol. Bukaan liang masukan dikawal oleh omboh. Seperti juga enjin empat lejang diesel, enjin dua lejang diesel juga tidak mempunyai palam pencucuh dan minyak diesel disuntik ke kebuk pembakaran pada penghujung lejang mampatan. Semasa omboh turun ke bawah sehingga membuka liang masukan, injap ekzos turut terbuka dan udara bersih dari liang masukan akan memaksa gas ekzos keluar, menjadikan gas ekzos enjin diesel dua lejang lebih bersih daripada enjin petrol dua lejang.

Walau bagaimanapun, enjin ini memerlukan pengecas super untuk berfungsi mengepam masuk udara bersih ke dalam enjin. Oleh itu, enjin diesel dua lejang yang dilengkapi pengecas super dianggap sebagai enjin pernafasan biasa. Di dalam sesetengah kes, enjin diesel dua lejang yang sedia dipasang dengan pengecas super boleh dipasang dengan pengecas turbo bagi meningkatkan kuasanya.

Enjin diesel dua lejang lazimnya digunakan dalam aplikasi berat seperti lokomotif kereta api, janakuasa elektrik serta sebagai enjin kapal.

Note: Untuk belajar dan mengetahui lebih lanjut berkenaan modifikasi jentera dua lejang anda sila dapatkan Buku Panduan Modifikasi yang telah kami keluarkan secara hard copy (buku) di SINI dan soft copy (download) di SINI.

Berita BAIK!!!..Buku Panduan Modifikasi - Hardcopy

2011-10-09T18:00:00.014+08:00

BUKU PANDUAN MODIFIKASI Y125 KINI DLM HARDCOPY/BOOKLET

Salam semua...oleh kerana sambutan yg amat menggalakkan serta permintaan yg tinggi...kini kami di Byetools, menyediakan Buku Panduan secara Hardcopy/booklet. Jadi bagi mereka yg mempunyai masalah utk membeli buku secara Ebook, kini anda boleh memilikinya dan Kami akan Pos ke alamat ada..seluruh Semenanjung Malaysia termasuk Sabah Sarawak...

Yang pastinya Buku Panduan ini dicetak dengan muka surat berwarna agar dapat membantu pemahaman dalam pembacaan anda.
Bantuan khidmat nasihat teknikal juga diberikan kepada anda yg telah memiliki buku Panduan ini....

Sedikit Gambar2 dari Buku:

Bagi mereka yg berada di Area KL - Petaling Jaya...anda boleh menghubungi wakil kami utk urusan COD (cash on delivery).

APE TUNGGU LAGI??...DARI KAMI..TERBAIK UNTUK ANDA...

Untuk Tempahan

Hubungi : Chaklek (KL) -0122053371
Bent (Sabah & Sarawak) - 0198246639

SELAMAT HARI RAYA - MAAF ZAHIR BATIN

2011-09-15T12:53:00.004+08:00

Salam Aidilfitri dan Maaf zahir batin....dari kami di Byetools....diam x diam dah 17 Syawal...so ade x masih dalam mood Raya??...haha...bagi yg xhabis2 pergi raya tue teruskan la ye...n bagi Riders2 diluar sana...racing2 jugak...safety first...

Bagi semua yg mahu berkomunikasi dengan lebih dekat dengan Kami, sila ke " GROUP OTAI TWO STROKE '' di Facebook. Disini kita boleh bertukar2 pendapat, bincangkan isu2 teknikal, isu2 setting, jual beli dan sebagainya. So jangan malu2 jom sertai kami.

CARBURETOR

2011-06-15T02:05:00.003+08:00

Intro

Carburetor tuning has the greatest effect on engine performance. When a motorcycle manufacturer builds a bike, they usually install jets in the carb that are too rich. The manufacturers sell the same model worldwide, so they couldn’t afford to install different jets in the carb to suit all the different climates and types of fuel. In addition to the climate and fuel, the manufacturer would also have to consider many other factors, such as the terrain and type of riding. And then there is the most important jetting consideration, the rider.

When I worked as a mechanic, I was in charge of jetting the bike over the course of the day. During morning practice sessions, the track was usually muddy and the air temperature was at its lowest point. I had to jet the bike rich for practice because the air density was
Adjusting the Carb...

Adjusting the Carb...

greater and the mud put more of a load on the engine. Then I had to watch the rider and the bike perform on different sections of the track. I would go to the obstacle on the track that presented the greatest load on the bike, typically an uphill straight section. I’d listen to my engine and watch the rider. I’d listen for pinging or knocking noises or excessive smoke from the pipe. I would watch to see if the rider had to fan the clutch a lot and how my bike pulled in comparison to others. Getting feedback from the rider is difficult because they are concentrating on riding not the bike’s performance. At a pro national there is one practice session, followed by a series of qualifiers and eventually two race motos. The time spacing of the riding sessions over the course of the day was such that I had to compensate the jetting two or three times. Otherwise, the bike would either seize from being too lean in the morning or run too rich for the second moto.

Race mechanics have different techniques for carb jetting. These techniques range from asking other mechanics what jets they are running to using precise measuring gauges to monitor the engine performance. In motocross races, where most of the riders are of equal skill levels, a holeshot in the start can mean the difference between a place on the podium and 30 minutes of roost in your face! The difference in horsepower between the bike that gets the holeshot and the bike that brings up the back of the pack may only be a few ponies! The race mechanic can give his rider an awesome advantage if he carefully monitors the carb jetting.

This section will give you insight into the carb tuning process, from diagnosing mechanical problems that mimic poor jetting to tuning tools such as gauges. It will also give you tips on a jetting method that I’ve developed called the “ride-and-feel” method,” which I consider to be the best method It’s a technique that I teach to all the riders I’ve worked with. You don’t need any fancy tools, just the ability to make observations while you ride.

The Differences in Two-Stroke and Four-Stroke Carbs
The difference between a two-stroke and four-stroke engine is intake velocity. Two-stroke engines have lower velocity so the needle jet has a half-moon shaped hood protruding into the venturi to produce a low pressure area that aids in drawing the fuel up through the needle jet. Four-stroke carbs need to atomize the fuel more so than a two-stroke carb because so much of the fuel shears along the intake port and separates from the mixture stream. Four-stroke carbs have more jets and finer adjustment screws, plus they usually are equipped with an accelerator pump. A typical state of the art four-stroke carb is the Keihin CR.

The latest trend in two-stroke carbs features a pump that sprays fuel into the venturi from 1/4th to 3/4th throttles. In the past, carb manufacturers made jet needles that attempted to compensate for the natural lean condition of the mid-range but that compromised the jetting at full throttle. The auxiliary pumps are powered by electricity supplied by the alternator (about 5 watts) and controlled by either a throttle position or an rpm sensor.

Identification Guide to Popular Carb Types
Keihin PWK Carburetor.

Keihin PWK Carburetor.

On two-stroke engines, several different model carbs have been used over the years, but there are basically two big carb manufacturers. Kehin and Mikuni are two popular brands of Japanese carbs used on nearly every dirt bike.

Kehin has several different models. The most popular ones are the PJ, PWK, and PWM. The PJ is used on Honda CR125, 250, and 500 models from 1985-1997 The slide is oval shaped and there are no additional pumps, and it’s just a simple carb. In fact it’s so simple that the choke and idle screw share the same jet. The PWK was the next step up from the PJ. The PWK has a crescent shaped slide and a separate idle circuit from the choke. The PWK is used on Kawasaki KX125, 250, and 500 models from 1990-97. The latest version of the PWK features a pump to supply extra fuel in the mid-range. The PWM is similar to the older PWK (no pump) and the overall length is shorter.

Mikuni has several different model carbs too. The original model VM had a round slide. There are many different parts available including needle jets of different diameters and jet needles with different taper angles and diameters. The next model was the TMX, which became available in 1987. It was a flat-slide carb, which offered a greater peak flow rate. The TMX was revised several times, becoming smaller with fewer parts. The TMS carb introduced in 1992 had no main or pilot jet. The slide and jet needle handled all the jetting. That carb worked great on 250cc bikes but never became popular. The PM is the latest Mikuni model. It features an oval crescent shaped slide and a very short body. That carb comes standard on Yamaha YZ125 and 250 1998 and newer models.

Carburetor Parts and Function
A carburetor is a device that enables fuel to mix with air in a precise ratio while being throttled over a wide range. Jets are calibrated orifices that take the form of parts such as pilot/slow jets, pilot air screw, throttle valve/slide, jet needle, needle jet/spray-bar, air jet, and main jet. Fuel jets have matching air jets, and these jets are available in many sizes to fine-tune the air-fuel mixture to the optimum ratio for a two-stroke engine, which is 12.5: 1.

Fuel Jets, Air Jets, and Throttle Positions
Three circuits control the air: the air-screw, the throttle slide, and the air jet. Four circuits control the fuel: the pilot/slow jet, the spray-bar/needle jet, the jet needle, and the main jet. The different air and fuel circuits affect the carb jetting for the different throttle-opening positions, as follows:

Closed to 1/8 throttle—air screw and pilot/slow jet

1/8 to 1/4 throttle—air-screw, pilot/slow jet, and throttle slide

1/4 to 1/2 throttle—throttle slide and jet needle

1/2 to full open—jet needle, spray-bar/needle jet, main jet, and air jet

(Note: On many modern carbs the spray-bar/needle jet and air jets are fixed-diameter passages in the carburetor body and cannot be altered.)

carb_jet_usage1

Basic Carb Service
Nobody likes to fiddle with a carb if they don’t have to. Wedged in between the engine and frame with tubes, cables, and wires sprouting out like spaghetti, carbs are a pain to work on. Carbs require cleaning just like anything else, and some careful observations can save you big money in the long run. Start by pressure washing the bike, especially around the bottom of the carb where roost from the tires and oil from the chain accumulate. Take care when removing the carb; it’s easy to damage the cable. It’s better to remove the sub-frame so as to enable unrestricted access to the carb. This will also make it easier to route the vent hoses in their proper positions too. When you remove the carb, look at the vent hoses. Are they melted from heat or clogged with mud? If so that can cause a vapor-locking problem in the float bowl and make the engine bog.

Remove the top of the carb and disconnect the cable from the slide. Is the cable frayed or kinked? Is the rubber dust cover missing? If so then replace the cable. Now remove the float bowl, jet baffle (white plastic shroud around main jet), float and fuel inlet needle, and the air-screw. Shake the floats and listen for fluid that may have seeped inside. If so, replace the floats otherwise the engine might suffer from constant fuel flooding. Check the fuel inlet needle. It has a Viton rubber tip and occasionally fuel additives and dirt damage the tip. Also check the spring-loaded plunger on the opposite end of the tip. If the spring doesn’t push the plunger all the way out then replace it. Check the air-screw, there should be a spring and o-ring on the end of the needle. The spring provides tension to keep the air-screw from vibrating outward and the o-ring seals out dirt and water from entering the pilot circuit. Next check the bell mouth of the carb. Look for the two holes at the bottom of the bell mouth. The one in the center is the air passage for the needle jet and the other hole offset from center is the air passage for the pilot circuit. It’s typical for those passages to get clogged with dirt and air filter oil. That would cause the engine to run rough because without a steady stream of air to mix with and atomize the fuel, raw fuel droplets make the jetting seem rich.

Once the carb is basically stripped down (pilot/slow and main jet still in place) you can flush the passages. Get an aerosol can of brake or carb cleaner from an auto parts store. Make sure you get the type with the small diameter plastic tube that attaches to the spray tip. Direct the tip into the airscrew passage. When you spray the cleaner you should see it flow out the pilot/slow jet and the air passage in the bell mouth. Next spray through the pilot/slow jet, look for flow through a tiny passage located between the venturi and the intake spigot. Spraying cleaner through these passages insures that the low speed air and fuel circuits are open and free flowing. The last area to flush with the carb cleaner is the slide bore and slide. Dirt tends to trap there, causing the mating surfaces to develop scratches that could cause the throttle to stick!

Just a small amount of water and dirt can get trapped in the tiny passages of the carb and cause havoc with jetting or even engine damage. How often should you service the carb? When it gets dirty! For example if you ride in muddy wet conditions you should at least check the vent hose. If the riding conditions are dusty and your air filter is covered with dirt, then it’s a good idea to do a basic carb servicing.

Mechanical Problems
The process of jetting—changing air or fuel jets in order to fine-tune engines’ performance—is very simple. Jetting becomes complicated because mechanical problems sometimes mimic improper jetting. This causes you to waste time and money trying to correct the problem with expensive carburetor jets.

Before you ever attempt to jet a carb, make sure the engine doesn’t have any of the problems in the following list. If you are in the process of jetting a carb and you are stumped with a chronic problem, use this section as a guide to enlightenment!

Crankcase air leaks—Air leaks can occur at the cylinder base, reed valve, or the magneto seal. Air leaks make the throttle response sluggish and may produce a pinging sound. That sound occurs when the air-fuel mixture is too lean.

Crankcase oil leaks—the right-side crankcase seal is submerged in the transmission oil. When this seal becomes worn, oil can leak into the crankcase. The oil is transferred up to the combustion chamber and burned with the air-fuel mixture. The oil causes the spark plug to carbon-foul. This mechanical problem makes the jetting seem to be too rich.
Check these for leaks.

Check these for leaks.

Coolant-system leaks—Coolant systems leaks commonly occur at the cylinder-head gasket. When the coolant leaks into the combustion chamber, it pollutes the air-fuel mixture and causes a misfire or popping sound at the exhaust pipe. Check the engine’s coolant level frequently. Hondas and Kawasaki’s have characteristic coolant leaks because they use steel head gaskets. Yamahas and Suzuki’s use O-rings to seal the head and cylinder. Coolant-system leaks lower the engine’s peak horsepower. It makes the engine run as if the air-fuel mixture is too rich.

Carbon-seized exhaust valves—the exhaust valves sometimes become carbon-seized in the full-open position. This mechanical problem can make the engine run flat at low rpm and make the slow-speed jetting seem lean. The carbon can be removed from the exhaust valves with oven cleaner. Clean the exhaust valves whenever you replace the piston and rings.

Blown silencer—when the fiberglass packing material blows out of the silencer, excess turbulence forms in the silencer and the turbulence causes a restriction in the exhaust system. This restriction makes the engine run flat at high rpm.

Broken reed-valve petals—the petals of the reed-valve can crack or shatter when the engine is revved too high. This mechanical problem makes the engine difficult to start and can also have a loss of torque. Expert rider should switch to carbon fiber reed petals because they resist breaking at high rpm. Novice riders should use dual-stage fiberglass reeds (Aktive or Boyesen). These types of reed petals provide an increase in torque.
Make sure the packing in your silencer has not been blown out. It makes a difference.

Make sure the packing in your silencer has not been blown out. It makes a difference.

Weak spark—when the ignition coils deteriorate, the engine performance will become erratic. Normally, the engine will develop a high-rpm misfire problem. Check the condition of the coils with a multimeter.

Clogged carburetor vent hoses—when the carburetor vent hoses get clogged with dirt or pinched closed, the jetting will seem to be too lean, so the engine will run sluggish. Always check the condition of your carburetor vent hoses. Make sure there is no mud in the hoses and that the hoses are not pinched between the suspension linkage.

Carburetor float level—when the float level is too low, the jetting will seem to be too lean. Engine performance will be sluggish. When the float level is too high, the jetting will seem to be too rich.

Worn carburetor fuel-inlet needle—when the fuel-inlet needle wears out, excess fuel enters the float bowl and travels up the slow jet and into the engine. This makes the carb jetting seem to be too rich. Replace the fuel-inlet needle and seat every two years.

Jetting Shouldn’t Be Scary!
Make sure you have a good selection of jets.

Make sure you have a good selection of jets.

Jetting is the process of making adjustments to the air and fuel jet sizes in order to fine tune the carburetion to suit the load demands on the engine and make the power delivery consistent and optimum. Too much anxiety is placed on jetting. Most people just want to call me on the phone and ask what jets they should put in their carb. That’s an impossible question because that the big dirt bike magazines attempt to answer just to increase readership. People get confused because they read jetting specs in a magazine, put those jets in their bike and seize the engine. Any quoted jetting in this book is just a baseline. Most magazines don’t list parameters for their jetting specs like; Brand new bike running with VP C-12 fuel with Silkolene oil mixed at 30:1 and a NGK 8 spark plug, ridden by a really slow lard-ass editor twisting the throttle on a hard-packed track. Some part numbers and jet sizes are given in the Tuning Tips section for models that definitely need certain jets in order to get the bike near the baseline. There is an old saying that says you can fish for a man and feed him for a day or teach him to fish and enable him to feed himself for life. Here is a quick lesson on how to jet your dirt bike.

The Ride and Feel Method
The most basic method of determining correct carburetor jetting is “ride and feel.” This method requires you to determine if the carburetor tuning is too rich or too lean by the sound and feel of the engine. The first step is to mark the throttle body in 1/4-throttle increments, from closed to full open. Then, this method requires that you ride the motorcycle on a flat, circular course. To check the carb jetting for throttle positions up to 1/2 throttle, ride the motorcycle in second or third gear. Roll on the throttle slowly from 1/4 to 1/2
Carburetor animation.

Carburetor animation.

open. If the engine is slow to respond and bogs (engine makes a booooowah sound) then the carb jetting is too lean. You can verify lean jetting by engaging the carb’s choke to the halfway position. This will make the air-fuel mixture richer and the engine should respond better. If the carb jetting is too rich, then the engine will make a crackling sound; the exhaust smoke will be excessive and the engine will run as if the choke is engaged. Careful engagement of the choke can help you determine if the jetting is rich or lean. Another important tip is to just change the jets one increment at a time, either rich or lean, until the engine runs better. Most people are afraid to change a jet because they think that the engine will be in danger of seizing. Believe me, one jet size won’t make your engine seize but it could be the difference between running bad and running acceptable.

To check the jetting for throttle positions from 1/2 to full open, ride the motorcycle in third and fourth gear. (You may need to increase the diameter of the circular riding course for riding in the higher gears.) Check the jetting in the same manner as listed above. The carb jets that affect the jetting from 1/2 to full throttle are the jet-needle, main jet, power jet (electronic carbs) and the air jet (on four-strokes).

If you want to take this technique out to the racetrack, you can test the pilot/slow jet when accelerating out of tight hairpin turns, the needle clip position on sweeper turns and short straits, and test the main jet on the big uphill or long straits. Of course be careful if you try to use the choke technique because you could lose control when riding one handed.

Jetting for Riding Techniques
Certain types of riders require jetting to compliment their technique. For example beginner minibike riders will need slightly richer jetting on the pilot/slow jet and the needle clip position to mellow the power band and make it easier to ride. Conversely desert racers who hold the throttle wide open for long periods of time need rich main jets to compensate for the high load.

The Weather Makes The Biggest Difference!
What are the conditions?The weather can have a profound affect on the carb jetting because of the changes in air density. When the air density increases, you will need to richen the air-fuel mixture to compensate. When the air density decreases, you will need to lean-out the air-fuel mixture leaner to compensate. Use the following as a guide to correcting your jetting when the weather changes:

Air temperature—when the air temperature increases, the air density becomes lower. This will make the air-fuel mixture richer. You must select jet sizes with a lower number to compensate for the lower air density. When the barometric pressure decreases, the opposite effect occurs.

Humidity—when the percentage of humidity in the air increases, the engine draws in a lower percentage of oxygen during each revolution because the water molecules (humidity) take the place of oxygen molecules in a given volume of air. High humidity will make the air-fuel mixture richer, so you should change to smaller jets.

Altitude—generallly, the higher the altitude, the lower the air density. When riding at racetracks that are at high altitude, you should change to smaller jets and increase the engine’s compression ratio to compensate for the lower air density.

Track Conditions and Load
The conditions of the terrain and the soil have a great affect on jetting because of the load on the engine. Obstacles like big hills, sand, and mud place a greater load on the engine that requires more fuel and typically richer jetting. In motocross, track conditions tend to change over the course of the day. Typically in the morning the air temperature is cooler and the soil wetter requiring richer jetting. In the afternoon when the temperature rises and the track dries out, leaner jetting is needed in order to keep the engine running at peak performance. Other changes for mud and sand riding might include changing to a lower final-drive ratio (rear sprocket with more teeth) to reduce the load on the engine and help prevent it from overheating. Advancing the ignition timing will make the engine more responsive at low to middle rpm.

Fuel and Oil Mixture Ratios
The simple, quick and easy way to get your pre-mix ratio correct. A Ratio Rite measuring cup.

The simple, quick and easy way to get your pre-mix ratio correct. A Ratio Rite measuring cup.

When we talk about the “fuel” in the air-fuel mixture for a two-stroke engine, we are really talking about a mixture of fuel and oil. If you richen the pre-mix ratio (20:1 as opposed to 30:1) there is more oil and less fuel in the same volume of liquid, which effectively leans the air-fuel ratio. And this fact gives the clever tuner one more tool to use when the correct jet is not available or when none of the standard jets are exactly right. You can richen the jetting by slightly reducing the pre-mix ratio (less oil). You can lean the jetting by increasing the pre-mix ratio (more oil). The best part is that changes in the pre-mix ratio affect the jetting over the entire throttle-opening range, but the changes in ratio must be small to prevent excess wear from lack of lubricating oil or fouled plugs from too much oil.

Pre-mix oils are formulated for a fairly narrow range of pre-mix ratios. You should examine the oil bottle for the oil manufacturer’s suggestion on the pre-mix ratio. All production two-stroke dirt bikes have a sticker on the rear fender suggesting that you set the pre-mix ratio to 20:1 That sticker is put there for legal purposes. Always refer to the oil manufacturer’s suggestion on pre-mix ratios. In general, small-displacement engines require a richer pre-mix ratio than do large-displacement engines because smaller engines have a higher peak rpm than larger engines. The higher the engine revs, the more lubrication it requires.

Tuning Gauges
There are three types of gauges that professional tuners use to aid carb jetting:

1. Relative-air-density (RAD) gauge

2. Air-fuel (AF) ratio meter

3. Exhaust-gas-temperature (EGT) gauge

The following is a description of how each gauge functions and their advantages.
Relative Air Density Guage from Tanner Racing

Relative Air Density Guage from Tanner Racing

RAD gauge—this is the best gauge for dirt bikes because of the convenience. The gauge is no good unless you get the jetting perfect once. The RAD gauge provides you with an indication of how much the air density changes, helping you compensate for the affects of changes in the air temperature, altitude, and barometric pressure. The gauge is calibrated in percentage points. Once you set the jetting with the ride and feel method, you can set the calibration screw on the gauge so the needle is pointing to 100 percent. When the air density changes, the RAD gauge will show the relative percent of change. Using a calculator you can multiply the percentage change shown on the RAD gauge by the jet size and determine the corrected jet size for the air density. The pilot/slow and main jet have number sizes that correlate with the RAD gauge, but the needle clip position can only be estimated. Normally for every two main jet increments, the needle clip must be adjusted one notch.
AF ratio meter from Innovate Motorsports

AF ratio meter from Innovate Motorsports

AF ratio meter—The AF meter measures the percentage of oxygen in the exhaust gasses, and displays the approximate air-fuel ratio of the carb. The gauge displays AF ratios from 10-16:1, the optimum AF ratio for a two-stroke engine is 12:1. The AF gauge utilizes a lambda sensor that is inserted into the center of the exhaust stream, approximately six inches from the piston in the header pipe of a four-stroke and in the baffle cone of a two-stroke engine. A permanent female pipe fitting (1/4in.) must be welded to the side of the exhaust pipe in order to fasten the sensor. The weld-on fitting set-up is also used on the temperature gauges, and the fitting can be plugged with a 1/4in. male pipe fitting when the gauge is not in use. This gauge is ideal for four-stroke engines.
EGT gauge by Digitron

EGT gauge by Digitron

EGT gauge—The EGT gauge measures the temperature of the gasses in the exhaust pipe by means of a temperature probe fastened into the exhaust pipe, six inches from the piston. This type of gauge enables you to tune the carb jetting and the pipe together, taking advantage of the fact that exhaust pipes are designed with a precise temperature in mind.

An exhaust pipe is designed to return a compression wave to the combustion chamber just before the exhaust port closes. Most pipes are designed for a peak temperature of 1,200 degrees Fahrenheit. Most dirt bikes are jetted too rich, which prevents the exhaust gasses from reaching their design temperature, so power output suffers. Sometimes just leaning the main jet and the needle-clip position makes a dramatic difference.

Digitron is the most popular brand of EGT gauge. It measures both EGT and rpm. This gauge is designed for go-kart racing so it’s not suited for wet weather conditions. It is designed to mount on the handlebars. That way the rider can focus in on it. Once you have performed the baseline jetting, send the rider out on the bike with the EGT. The rider observes the EGT to give you feedback on the necessary jetting changes. Once the jetting is dialed, we use the tachometer to check the peak rpm of the engine on the longest straight of the racetrack. For example, if the peak rpm exceeds the point of the engine’s power-peak rpm, then change the rear sprocket to a higher final-drive ratio (rear sprocket with fewer teeth) until the rpm drops into the target range. An EGT gauge is ideal for dirt track bikes and go-karts, where peak rpm temperature is critical.

The article above is all about two stroke carburetor tuning and yet was found on a web site devoted to Street Bikes. Go figure! This is the site that I found it on http://hondanighthawks.net/carb16.htm

- twostrokemotocross

JOM LAYAN DRAG!!!!!

2011-06-10T14:31:00.002+08:00

E-BOOK PANDUAN MODIFIKASI YAMAHA 125Z - EDISI PERTAMA

2011-05-08T14:28:00.026+08:00

-PRAKATA-

Buku Panduan ini amat sesuai kepada mereka yang baru menceburi bidang ini dan sesiapa yang berminat untuk mempelajari dan mendalami teknik modifikasi enjin 2 lejang, khususnya enjin motosikal Yamaha 125z. Panduan yang harus dimiliki semua peminat 125z. Penggunaan bahasa yang lebih ringkas, santai dan campuran bahasa yang biasa digunakan oleh mekanik-mekanik dan mereka yang arif dalam bidang ini dan untuk memudahkan lagi pemahaman anda.

ISI KANDUNGAN

BAB 1

FORMULA PEMBAKARAN
KONSEP PERGERAKAN ENJIN 2 LEJANG
PERINGKAT-PERINGKAT MODIFIKASI

BAB 2

8 BAHAGIAN UTAMA MODIFIKASI
KABURATOR
REEDVALVE(REVAB)
SILINDER BLOK(PORTING TEKNIK)
PISTON-PISTON
KEPALA SILINDER(HEAD SQUISHBAND)
SISTEM PENYALAAN
CLUTCH(CEKAM)
EKZOS

BAB 3

BAHAGIAN MODIFIKASI TAMBAHAN
GEAR BOX(KOTAK GEAR)
BEARING(ALAS BEBOLA)
MAGNETO
CON ROD(ROD PENYAMBUNG)
COIL PLUG(GELUNG PENCUCUH)

TIP-TIP

SET UP KABURATOR
RIDER & GEAR SHIFT TEKNIK
SERVIS & PRODUK
CONTACT
KESIMPULAN
PENUTUP

Contoh Blok Mapping untuk 57mm Blok

APA YANG ANDA PELAJARI SETELAH MEMILIKI PANDUAN INI

>ANDA INGIN TAHU FUNGSI-FUNGSI KOMPONEN 125Z?
>ANDA INGIN TAHU KOMPONEN UTAMA YANG BOLEH MEMBERI PERUBAHAN KETARA PADA KUASA ENJIN ANDA?
>ANDA INGIN TAHU PERINGKAT-PERINGKAT MODIFIKASI?
>ANDA INGIN TAHU JENIS-JENIS,PERBEZAAN,DAN TEKNIK-TEKNIK PENGUBAHSUAIN KABURATOR?
>ANDA INGIN TAHU TEKNIK-TEKNIK TUNING BERDASARKAN PLUG READING?
>ANDA INGIN TAHU JENIS-JENIS BLOK, TEKNIK-TEKNIK PORTING(KOREK BLOK),CARA-CARA MENDAPATKAN PETA BLOK, PERBEZAAN TEKNIK PORTING DAN SEBAGAINYA?
>ANDA INGIN TAHU TEKNIK PENGUBAHSUAIAN,MEMBUAT UKURAN,PENGIRAAN,UBAHSUAI DOME(KAWAH),SQUISHBAND?
>ANDA INGIN TAHU CARA PENGIRAAN GEAR RATIO(NISBAH GEAR ,JENIS2 GEAR?

DAN BANYAK LAGI YANG MENARIK UTK MEMBANTU ANDA DALAM MEMANTAPKAN LAGI PENGETAHUAN DIDALAM BIDANG MODIFIKASI.......JANGAN LEPASKAN PELUANG INI!!!!!!! DAPATKAN SEGERA SEBELUM TERLAMBAT!!

TUNGGU DULU!!!!ANDA JUGA AKAN MENERIMA BONUS ISTIMEWA PERCUMA DARI KAMI, IAITU " EBOOK 2STROKE TUNING GUIDE" YANG BERNILAI(RM150) APABILA ANDA MEMBUAT PESANAN DALAM( MASA 7HARI) MULAI HARI INI!!!

SEMUA INI AKAN JADI MILIK ANDA HANYA DENGAN HARGA ISTIMEWA-
( RM50 SAHAJA)......APA TUNGGU LAGI!!!BERTINDAK SEBELUM TERLAMBAT!!

APA KATA MEREKA-

1.Dengan panduan ini saya banyak mempelajari teknik-teknik yang betul utk mengubahsuai enjin 125z saya.....Amat berbaloi... (Azam - kedah)

2.Kepada mereka yang ingin menceburi bidang ini ,saya wajibkan anda dapatkan panduan ini,banyak yang anda boleh pelajari didalam panduan ini..... (Amat - melaka)

3.Setelah saya mencuba teknik yang diajarkan,kuasa dan kelajuan enjin motosikal 125z saya semakin bertambah...........Saya amat berpuashati...(joseph -sarawak)

4.Senang dihubungi..email cepat dapat...n pomen pon sempoi..xsabar nak tunggu Buku edisi ke-2.. (Bobby - Cheras)

5.Saya dapat mempelajari basic modify untuk jentera kesayangan saya nie..Thumb ups..Byetools (Wan - seremban)

6."walaupon masih baru pakai 125z,saya dapat belajar banyak perkara khasnya parts2 yg perlu di modify...utk tambah performance..xsabar nak tunggu buku edisi kedua.." - (Momo - Pahang)

7.Buku yg bagus...teliti dan ditulis oleh pomen yg berpengalaman...semua perkara diterangkan secara details. (hafiz - melaka)

.ANDA BILA LAGI????BUAT PESANAN SEKARANG!!!

DAPATKAN SEKARANG!!!!! lebih 50 ebook telah dijual..

Untuk tempahan dan maklumat lanjut sila hubungi :

0122725253 (Bye), - Melaka
0122053371 (chaklek) - Kuala Lumpur
0198246639 (Bent) - Sabah/Sarawak

UNTUK PESANAN TERUS

SILA BUAT PEMBAYARAN KE AKAUN MAYBANK-(112223009915-BRYAN MORRISON)
BERJUMLAH RM50,SELEPAS ITU SILA SMS-TAIP{email anda}{nama anda}{no hp anda}{masa bank in} KE-019-8246639. SEMUA PESANAN AKAN DIPROSES SELEPAS PENGESAHAN PEMBAYARAN DIBUAT DALAM MASA -(24 JAM).PEMBERITAHUAN MELALUI SMS AKAN DILAKUKAN SETELAH PENGHANTARAN PESANAN DIBUAT KE EMAIL ANDA.

TERIMA KASIH.

KHIDMAT MODIFIKASI JENTERA 2-LEJANG ANDA

2011-05-08T13:39:00.008+08:00

Terdapat untuk pelbagai model seperti, 125z,RxZ,Panther,TZM…dll….juga utk event2 sepeti Drag, Cuprix dan off-road

A) Pakej Standard Modified: RM???

- Porting blok ,head, carbs, siap setting….sesuai utk mereka yg inginkan Spec standard (Ekzos Standard)…free tutorial for “Blok Maping”…call for more details…

B) Pakej Beginner (Big Bore tuning) RM???

- Pakej ini adalah gabungan dari Pakej Standard Modified yang mana, Blok anda akan Reseleeve, Extra porting…racing boss clutch…

- Anda boleh memilih pelbagai jenis2 Carbs yg sesuai dgn citarasa anda utk pakej ini dan seterusnya…

C) Pakej Advance (Big Bore + Stroking) RM???

- Pakej ini utk Stroking @Jekrod, dalam pakej nie…sudah semestinya kami akan Setting Port-Timing, advance tuning utk Blok..

- Advance setting utk ekzos chamber/cutting standard (paip tipu)

- Setting speed with Velo8 Speed meter…
- Reed valve tuning

D) Pakej Open modified RM???

- Spec Open modified yg membolehkan jentera anda utk event…seperti Drag…dan H***way..

- Full racing spec … Blok,Head, carbs, Ekzos, Gearbox, Clucth, Bearing…dan byk lagi call for details..

BYETOOLS vs KERE PASIR MAS 18k

2010-09-10T20:04:00.001+08:00

BYETOOLS & EMY SUTUN KB

2010-09-10T19:50:00.003+08:00

MAT REMPIT LANGGAR LEMBU... MANGSA KEADAAN

2010-08-24T20:53:00.001+08:00

VALENTINO ROSSI 'YAMAHA ATAU DUCATI' ?

2010-08-24T04:39:00.001+08:00

BRNO, (Czech Republic): Juara dunia tujuh kali MotoGP, Valentino Rossi menandatangani kontrak dua tahun berlumba untuk pasukan Ducati, kelmarin.

Rossi, penunggang Yamaha akan menggantikan bekas juara dunia dari Australia, Casey Stoner yang akan bersama Honda musim depan selepas menamatkan kontrak empat tahun bersama pasukan Itali itu.

Rossi berkata dia mencari cabaran baru selepas tujuh tahun bersama pengeluar jentera dari Jepun.

“Masanya sudah tiba untuk saya mencari cabaran baru; kerja saya bersama Yamaha kini berakhir,” kata Rossi.

“Memang menyedihkan apabila segala cerita indah berakhir, tapi mereka meninggalkan kenangan mendalam.” Rossi, 31, menamatkan GP Czech di kedudukan kelima Ahad lalu, tetapi peluangnya untuk mengekalkan kejuaraan dunia sudah berakhir selepas dia berehat selama enam minggu akibat patah kaki pada kemalangan yang dialaminya di litar Mugello.

“Kami dengan gembiranya mengumumkan bahawa Valentino Rossi akan bersama kami bermula 2011,” kata Presiden Ducati, Gabriele Del Torchio.

“Dia satu lambang keunggulan dalam kecemerlangan dunia permotoran.” Pengarah Urusan Yamaha Mtor Racing, Lin Jarvis pula berkata, Rossi memainkan peranan penting menaikkan pasukan.

“Valentino menyertai Yamaha pada 2004 ketika pasukan bergelut selepas 11 musim tanpa kejayaan,” kata Jarvis.

“Kejayaan pertama Valentino buat Yamaha adalah di Afrika Selatan pada 2004, itulah saat-saat paling menggembirakan dan ia menjadi perlumbaan sebelum dia mencatat lebih banyak kejuaraan di seluruh dunia selain diminati ramai,” katanya. -AFP

BYETOOLS vs YUNUS (SEREMBAN) 5k

2010-08-11T05:23:00.004+08:00

BYETOOLS vs EDY (seremban)

2010-07-30T23:12:00.004+08:00

BYETOOLS vs ABOL aka AS MOTOR

2010-07-28T15:17:00.003+08:00

RXZ CLUTH PLATE 100% ORI FCC

2010-07-03T12:02:00.004+08:00

Pastikan cluth plate yg ori.

Masalah selalu timbul bila kita mengunakan componen tiruan. Cluth plate tiruan tidak akan berfungsi dengan cekap dan kesannya, ia akan membatasi kelajuan motor anda. Tanpa ilmu dan pengalaman kita akan mudah ditipu oleh kedai spare parts atau bengkel yang tak jujur.

Antara masalah yg akan anda hadapi apabila menggunakan cluth plate tiruan: Motorsikal anda tidak boleh mengunakan 4T base on synthetic. Maksudnya disini anda tidak dapat mengunakan minyak pelincir fully synthetic untuk memanjangkan jangka hayat komponen motorsikal anda.

Kesan bila anda mengunakan minyak pelincir base on synthetic kepada cluth plate tiruan: Anda akan terasa seperti kehausan pada cluth plate (Pick up takde).

Di bawah ini adalah contoh cluth plate ori yang ada dalam stock kami.

Untuk mendapatkan FCC 100% Ori cluth plate.. sila hubungi kami...

Jangan tertipu ...!!! Rupa sama kualiti berbeza...!!! Dapatkan segera hanya dari kami..!!!! Terbaik dari ladang... !!! hehehehe....

RIDER POWER

2010-07-03T10:42:00.003+08:00

Rider aku rileks ajer.....

MIMC CHAMPIONS

2010-06-30T02:58:00.007+08:00

Gambar owner motor dan medal champion masa race kat MIMC dalam class special. Gambar rider cap ayam lupa nak ambik.. lain kali jer ler.. hehehe

No 1 dan No 4

nie jer yg ade lain xde....

Signal pun dah terkulai.. mcm ni pun boleh champion..

Sikit hari kalau minyak naik harga lagi aku pun pakai mcm ni kot..

SPRINT TEST PREPARATION 3

2010-06-08T14:08:00.005+08:00

50% SIAP

STANDARD MODY

EX5, 125Z dan KATOK

SETTING JANGAN TAK SETTING

RIDER n POMEN

SPRINT TEST PREPARATION 2

2010-06-08T13:49:00.003+08:00

BZ...

SEMUA MAU KASI SIAP..

POMEN MERANGKAP RIDER...

COMET..

SUPER VISOR

SPRINT TEST PREPARATION

2010-06-08T13:27:00.004+08:00

SENJATA TERPENTING...!!!

BLOCK RXZ 135

MOTUL 300V... MAHAL OOOOOiii...!!!

OVERHOUL

UMA RACING 34mm

TAMBAH KELAJUAN MOTORSIKAL

2010-05-26T23:20:00.003+08:00

Perkhidmatan modifikasi motorsikal anda

Hi tech

- Kami sebuah bengkel di Melaka menawarkan khidmat modifikasi motosikal anda.
- 2 lejang seperti RXZ, 125z, TXR, TZM dll.atau
- 4 lejang seperti KRISS, EX5, LC135 SUZUKI FX dll.
- untuk kegunaan harian ataupun dilitar (drag/cubprix).
- Harga boleh dirunding bergantung kepada tahap modifikasi.

- Segala modifakasi dilakukan dengan teknologi terkini selaras dengan kemajuan komputer.

Kami akan pastikan anda tidak akan keciwa dengan perkhidmatan kami. Jaminan wang dikembalikan jika pelanggan tidak berpuas hati dengan perkhidmatan yang kami beri.

Hiway and Cub Prix

Hi Way

Drag RXZ

Ada berani ka?

Untuk maklumat lanjut hubungi kami di no:
Tel: 0173068302 (bye)
Email: rubber_tapperz@yahoo.com
Blog: http://byeracing.blogspot.com

PETRONAS CUB PRIX KELUANG 2007

2009-12-26T13:07:00.004+08:00

BYETOOLS RXZ DRAGSTER

2009-12-26T12:57:00.003+08:00

BASIC 2 STROKE TUNING

2009-12-26T12:35:00.004+08:00

by ByeTools Hypertech Work

Changing the power band of your dirt bike engine is simple when you know the basics. A myriad of different aftermarket accessories is available for you to custom tune your bike to better suit your needs. The most common mistake is to choose the wrong combination of engine components, making the engine run worse than stock. Use this as a guide to inform yourself on how changes in engine components can alter the powerband of bike's engine. Use the guide at the end of the chapter to map out your strategy for changing engine components to create the perfect power band.

TWO-STROKE PRINCIPLES
Although a two-stroke engine has less moving parts than a four-stroke engine, a two-stroke is a complex engine because it relies on gas dynamics. There are different phases taking place in the crankcase and in the cylinder bore at the same time. That is how a two-stroke engine completes a power cycle in only 360 degrees of crankshaft rotation compared to a four-stroke engine which requires 720 degrees of crankshaft rotation to complete one power cycle. These four drawings give an explanation of how a two-stroke engine works.

1) Starting with the piston at top dead center (TDC 0 degrees) ignition has occurred and the gasses in the combustion chamber are expanding and pushing down the piston. This pressurizes the crankcase causing the reed valve to close. At about 90 degrees after TDC the exhaust port opens ending the power stroke. A pressure wave of hot expanding gasses flows down the exhaust pipe. The blow-down phase has started and will end when the transfer ports open. The pressure in the cylinder must blow-down to below the pressure in the crankcase in order for the unburned mixture gasses to flow out the transfer ports during the scavenging phase.

2) Now the transfer ports are uncovered at about 120 degrees after TDC. The scavenging phase has begun. Meaning that the unburned mixture gasses are flowing out of the transfers and merging together to form a loop. The gasses travel up the back side of the cylinder and loops around in the cylinder head to scavenge out the burnt mixture gasses from the previous power stroke. It is critical that the burnt gasses are scavenged from the combustion chamber, in order to make room for as much unburned gasses as possible. That is the key to making more power in a two-stroke engine. The more unburned gasses you can squeeze into the combustion chamber, the more the engine will produce. Now the loop of unburned mixture gasses have traveled into the exhaust pipe's header section. The gasses aren't lost because a compression pressure wave has reflected from the end of the exhaust pipe, to pack the unburned gasses back into the cylinder before the piston closes off the port. This is the unique super-charging effect of two-stroke engines. The main advantage of two-stroke engines is that they can combust more volume of fuel/air mixture than the swept volume of the engine. Example: A 125cc four-stroke engine combusts about 110cc of F/A gasses but a 125cc two-stroke engine combusts about 180cc of F/A gasses.

3) Now the crankshaft has rotated past bottom dead center (BDC 180 degrees) and the piston is on the upstroke. The compression wave reflected from the exhaust pipe is packing the unburned gasses back in through the exhaust port as the piston closes off the port the start the compression phase. In the crankcase the pressure is below atmospheric producing a vacuum and a fresh charge of unburned mixture gasses is flowing through the reed valve into the crankcase.

4) The unburned mixture gasses are compresses and just before the piston reaches TDC, the ignition system discharges a spark causing the gasses to ignite and start the process all over again.

CYLINDER PORTING
The cylinder ports are designed to produce a certain power characteristic over a fairly narrow rpm band. Porting or tuning is a metal machining process performed to the cylinder ports (exhaust & transfers) that alters the timing, area size, and angles of the ports in order to adjust the power band to better suit the rider's demands. For example, a veteran trail rider riding an RM250 in the Rocky mountain region of the USA will need to adjust the power band for more low end power because of the steep hill climbs and the lower air density of higher altitudes. The only way to determine what changes will be needed to the engine is by measuring and calculating the stock engine's specifications. The most critical measurement is termed port-time-area. This term is a calculation of a port's size area and timing in relation to the displacement of the engine and the rpm. Experienced tuners know what the port-time-area values of the exhaust and transfer ports should be for an engine used for a particular purpose. In general, if a tuner wants to adjust the engine's power band for more low to mid range he would do the following things. Turn down the cylinder base on a lathe to increase the effective stroke (distance from TDC to exhaust port opening). This also retards the exhaust port timing and shortens the duration and increases the compression ratio. Next the transfer ports should be narrowed and re-angled with epoxy to reduce the port-time-area for an rpm peak of 7,000 rpm. The rear transfer ports need to be re-angled so they oppose each other rather than pointing forward to the exhaust port. This changes the loop scavenging flow pattern of the transfer ports to improve scavenging efficiency at low to mid rpm (2,000 to 5,000 rpm). An expert rider racing mx in England would want to adjust the power band of an RM250 for more mid to top end power. The cylinder would need to be tuned radically different than for trail riding.
Here is an example. The exhaust port would have to be raised and widened to change the port-time-area peak for a higher rpm (9,000 rpm). For either of these cylinder modifications to be effective, other engine components would also need to be changed to get the desired tuning effect.

CYLINDER HEAD
Cylinder heads can be reshaped to change the power band. Generally speaking, a cylinder head with a small diameter and deep combustion chamber, and a wide squish band (60% of the bore area). Combined with a compression ratio of 9 to 1 is ideally suited for low to mid range power. A cylinder head with a wide shallow chamber and a narrow squish band (35-45% of bore area) and a compression ratio of 8 to 1, is ideally suited for high rpm power.
There are many reasons why a particular head design works for certain types of racing. For example; a head with a wide squish band and a high compression ratio will generate high turbulence in the combustion chamber. This turbulence is termed Maximum Squish Velocity, MSV is rated in meters per second (m/s). A cylinder head designed for supercross should have an MSV rating of 28m/s. Computer design software is used to calculate the MSV for head designs. In the model tuning tips chapters of this book, all the head specs quoted have MSV ratings designed for the intended power band changes.

CRANKSHAFT
There are two popular mods hop-up companies are doing to crankshafts; stroking and turbo-vaning. Stroking means to increase the distance from the crank center to the big end pin center. There are two techniques for stroking crankshafts; weld old hole and re-drill a new big end pin hole, or by installing an off-set big end pin. The method of weld and re-drilling is labor intensive. The off-set pin system is cheap, non-permanent, and can be changed quickly. In general, increasing the stroke of a crankshaft boosts the mid range power but decreases the engine's rpm peak.
The term "Turbo-Crank" refers to a modification to the crankshaft of a two-stroke engine, whereby scoops are fastened to the crank in order to improve the volumetric efficiency of the engine. Every decade some hop-up shop revives this old idea and gives it a trendy name with product promises that it can't live up to. These crank modifications cause oil to be directed away from the connecting rod and often times the vanes will detach from the crank at high rpm, causing catastrophic engine damage. My advice, don't waste the $750!

CARBURETOR
In general a small diameter carburetor will have high velocity and a good flow characteristic for a low to mid rpm power band. A large diameter carburetor works better for high rpm power bands. For 125 cc engines a 34mm carburetor works well for supercross and enduro and a 36 or 338 mm carburetor works best for fast mx tracks. For 250 cc engines a 36 mm carburetor works best for low to mid power bands and a 39.5 mm carburetor works best for top end power bands. Recently there has been a trend in the use of air-foils and rifle-boring for carbs. These innovations are designed to improve air flow at low throttle openings. Some companies sell carb inserts, to change the diameter of a carb. Typically a set of inserts is sold with a service of over boring the carb. For example; a carb for a 250cc bike (38mm) will be bored to 39.5mm and two inserts will be supplied. The carb can then be restricted to a diameter of 36 or 38mm.

REED VALVE
Think of a reed valve like a carburetor, bigger valves with large flow-areas work best for high rpm power bands. In general, reed valves with six or more petals are used for high rpm engines. Reed valves with four petals are used for dirt bikes that need strong low end and mid range power. There are three other factors to consider when choosing a reed valve. The angle of the reed valve, the type of reed material, and the petal thickness. The two common reed valve angles are 30 and 45 degrees. A 30-degree valve is designed for low to mid rpm and a 45 degree valve is designed for high rpm. There are two types of reed petal materials commonly used, carbon fiber and fiberglass. Carbon fiber reeds are lightweight but relatively stiff (spring tension) and designed to resist fluttering at high rpm. Fiberglass reeds have relatively low spring tension so they instantly respond to pressure that changes in the crankcase, however the low spring tension makes them flutter at high rpm thereby limiting the amount of power. Fiberglass reed petals are good for low to mid power bands and carbon fiber reeds are better for high rpm engines.
Boyesen Dual Stage reeds have a large thick base reed with a smaller thinner reed mounted on top. This setup widens the rpm range where the reed valve flows best. The thin reeds respond to low rpm and low frequency pressure pulses. The thick reeds respond to higher-pressure pulses and resist fluttering at high rpm. A Boyesen RAD valve is different than a traditional reed valve. Bikes with single rear shocks have off-set carbs. The RAD valve is designed to redistribute the gas flow to the crankcases evenly. A RAD valve will give an overall improvement to the power band. Polini of Italy makes a reed valve called the Supervalve. It features several mini sets of reeds positioned vertically instead of horizontally like conventional reed valves. These valves are excellent for enduro riding because of improved throttle response. In tests on an inertia chassis dyno show the Supervalve to be superior when power shifting. However these valves don't generate greater peak power than conventional reed valves. Supervalves are imported to America and sold by Moto Italia in Maine.

EXHAUST PIPE
The exhaust pipe of a two-stroke engine attempts to harness the energy of the pressure waves from combustion. The diameter and length of the five main sections of a pipe, are critical to producing the desired power band. The five sections of the pipe are the head pipe, diffuser cone, dwell, baffle cone, and the stinger. In general, after market exhaust pipes shift the power band up the rpm scale. Most pipes are designed for original cylinders not tuned cylinders. Companies like MOTOWERKS custom computer design and fabricate pipes based on the cylinder specifications and the type of power band targeted.

SILENCER
Silencers come in all sorts of shapes and sizes. A long silencer with a small diameter enhance the low to mid power because it increases the bleed-down pressure in the pipe. A silencer with a short length and a large core diameter provides the best bleed-down pressure for a high rpm engine. Too much pressure in the pipe at high rpm will radically increase the temperature of the piston crown and could cause the piston to seize in the cylinder.

FLYWHEEL WEIGHTS
The flywheel is weighted to improve the engine's tractability at low to mid rpms. There are two different types of flywheel weights, weld-on and thread-on. A-Loop performs the weld-on flywheel weight service. Steahly makes thread-on flywheel weights. This product threads onto the fine left-hand threads that are on the center hub of most Japanese magneto rotors. normally the threads are used for the flywheel remover tool. Thread-on flywheel weights can only be used if the threads on the flywheel are in perfect condition. The advantage to weld-on weights is they can't possibly come off.
External rotor flywheels have a larger diameter than internal rotor flywheels so they have greater flywheel inertia. Internal rotor flywheels give quicker throttle response.

AFFECTS OF THE IGNITION TIMING
Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.
Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.

HOW TO ADJUST THE TIMING
Rotating the stator plate relative to the crankcases changes the timing. Most manufacturers stamp the stator plate with three marks, near the plate's mounting holes. The center mark is the standard timing. If you loosen the plate mounting bolts and rotate the stator plate clockwise to the flywheel's rotation, that will advance the ignition timing. If you rotate the stator plate counterclockwise to the flywheel's rotation, that will retard the ignition timing. Never rotate the stator plate more than .028in/.7mm past the original standard timing mark. Kawasaki and Yamaha stator plates are marked. Honda stators have a sheet metal plate riveted to one of the mount holes. This plate insures that the stator can only be installed in one position. If you want to adjust the ignition timing on a Honda CR, you'll have to file the sheet metal plate, with a 1/4in rat-tail file.

AFTERMARKET IGNITIONS
The latest innovation in ignition systems is an internal rotor with bolt-on discs that function as flywheel weights. PVL of Germany makes these ignitions for modern Japanese dirt bikes. Another advantage to the PVL ignition is that they make a variety of disc weights so you can tune the flywheel inertia to suit racetrack conditions.
MSD is an aftermarket ignition component manufacturer. They are making ignition systems for CR and RM 125 and 250. MSD's ignition system features the ability to control the number of degrees of advance and retard. These aftermarket ignition systems sell for less than the OEM equivalent.

TIPS FOR BIG BORING CYLINDERS
In the mid nineties, European electro-plating companies started service centers in America. This made it possible to over bore cylinders and electro-plate them to precise tolerances. This process is used by tuners to push an engine's displacement to the limit of the racing class rules, or make the engine legal for a different class.
When you change the displacement of the cylinder, there are so many factors to consider. Factors like; port-time-area, compression ratio, exhaust valves, carb jetting, silencer, and ignition timing. Here is an explanation of what you need to do when planning to over bore a cylinder.
Port-Time-Area - This is the size and opening timing of the exhaust and intake ports, versus the size of the cylinder and the rpm. When increasing the displacement of the cylinder, the cylinder has to be bored to a larger diameter. The ports enter the cylinder at angles of approximately 15 degrees. When the cylinder is bore is made larger, the transfer ports drop in height and retard the timing and duration of those ports. The exhaust port gets narrower. If you just over bored and plated a cylinder, it would have much more low end power than stock. Normally tuners have to adjust the ports to suit the demands of the larger engine displacement. Those exact dimension changes can be determined with TSR's Time-Area computer program.
Cylinder Head - The head's dimensions must be changed to suit the larger piston. The bore must be enlarged to the finished bore size. Then the squish band deck height must be set to the proper installed squish clearance. The larger bore size will increase the squish turbulence so the head's squish band may have to be narrowed. The volume of the head must be increased to suit the change in cylinder displacement. Otherwise the engine will run flat at high rpm or ping in the mid range from detonation.
Exhaust Valves - When the bore size is increased, the exhaust valve to piston clearance must be checked and adjusted. This pertains to the types of exhaust valves that operate within close proximity of the piston. If the exhaust valves aren't modified, the piston could strike the valves and cause serious engine damage.
Carb - The piston diameter and carb bore diameter are closely related. The larger the ratio between the piston size and the carb size, the higher the intake velocity. That makes the jetting richer. Figure on leaning the jetting after an engine is over bored.
Ignition Timing - The timing can be retarded to improve the over rev. Normally over bored engines tend to run flat on top end.
Pipe and Silencer - Because only the bore size is changed, you won't need a longer pipe only one with a larger center section. FMF's line of Fatty pipes work great on engines with larger displacement. Some riders use silencers that are shorter with larger outlets to adjust the back-pressure in the pipe for the larger engine displacement.

KENANGAN

2009-08-12T14:58:00.000+08:00

SPRINT TEST GANGSA

2009-08-08T01:49:00.015+08:00

MONZA RALLY SHOW 2OO5 - VALENTINO ROSSI vs MC RAE

2009-08-02T12:20:00.001+08:00

NEW READ MORE

2009-08-01T16:57:00.003+08:00

Assalamualaikum..

Pasal blog lagi ni.. mintak sahabat2 ambil perhatian.. berkenaan tentang Read More . Seperti yg kita tahu banyak cara nak buat Read More ni. Tapi the latest Read More ialah mcm yg aku guna skrg ni. Kira lama jugak la aku dah guna Read More ni. tapi sebelum aku jumpa "[+/-] Read More" ni, aku guna jugak macam yg lama. Tp yg jenis ni hanya boleh diguna pada new templates jer. pada classsic template x dpt den nak nolong. Read More ni memang cukup2 bagus klau kita aplikasikan pada blog kita. Bagusnya apabila kita click pada [+/-]Read more ni, baki tulisan dari posting kita tu akan terus kluar tanpa perlu window mereload semula page kita. Selain itu , untuk posting yg pendek kita boleh hilangkan tulisan [+/-]Read more tu. Xder la org ingat masih ada posting yg tertinggal lagi. Dah la window nak kena reload semula, rupanya memang sampai situ jer posting kita.. hampehh.. mesti pelawat2 blog kita benggang kan. Mcm biasa.. klau kita guna [+/-]Read More jenis ni, pelawat2 blog kita yg internetnya slow mcm kura2 mesti suka dan berterima kasih pada tuan punya blog. Pelawat2 tentu akan merasa gembira segembira tuan punya blog jugak.. wakakaka..

Kat sini aku try buat tutor dia.. memang ada leceh sikit bagi yg kira newbie.. tp klau x cuba mana nak tau kan.. lebih baik gagal setelah mencuba daripada langsung xnak mencuba.
ok.. teruskan..

1. Sig in di blogger dengan id korang
2. Klik menu layout
3. Klik menu Edit HTML
4. Klik pada Full Download Template , sila save dulu template korang, proses ni bertujuan untuk kembalikan semula pada keadaan asal jika korang buat silap dalam proses editing template
5. Berikan tanda pada kotak kecil yang ada tulisan Expand Template Widget
6. Tunggu beberapa saat
7.Cari code </head>. kalau dah jumpa, copy kode kat bawah ni plak (yg warma merah), pastu pastekan selepas kode </head> yang korang dah jumpa tu tadi.

<script type='text/javascript' src='http://amen24.googlepages.com/Readmore.js' />
8. Tambahkan kode kat bawah ni pada kode template korang. Yang berwarna hitam tu adalah kode ori yang memang dah ada pada kode template korang, dan yang berwarna merah adalah kode yang korang kena tambah :

<h3 class='post-title'>
<b:if cond='data:post.url'>
<a expr:href='data:post.url'><data:post.title/></a>
<b:else/>
<data:post.title/>
</b:if>
</h3>
</b:if>
<div class='post-header-line-1'/>
<div class='post-body' expr:id='"post-" + data:post.id'>
<b:if cond='data:blog.pageType == "item"'>
<p><data:post.body/></p>
<b:else/>
<style>#fullpost {display:none;}</style>
<p><data:post.body/></p>
<span id='showlink'>
<p><a expr:onclick='"javascript:showFull(\"post-" + data:post.id + "\");"' href='javascript:void(0);'>[+/-] Read More...</a></p>
</span>
<span id='hidelink' style='display:none'>
<p><a expr:onclick='"javascript:hideFull(\"post-" + data:post.id + "\");"' href='javascript:void(0);'>[+/-] Read Less...</a></p>
</span>
<script type='text/javascript'>checkFull("post-" + "<data:post.id/>")</script>
</b:if>
<div style='clear: both;'/> 
</div>
</div>
.... rest of template code ....

9. Klik pada SAVE TEMPLATES

Langkah seeterusnya :
1. Klik menu Setting

2. Klik menu Formatting

3. Copy kode kat bawah ni dan paste pada ruangan Post Template

<span id="fullpost">

</span>

4. Klik pada Save Setting

5. Selesai.

Cara posting artikel :

Masa korang nak buat posting , click pada Edit HTML jangan pilih Compose, maka akan secara automatik terlihat kode tadi, yaitu :

<span id="fullpost">

</span>

Letak sedikit artikel korang sebelum kode <span id="fullpost">, dan artikel selebihnya korang letak selepas kode <span id="fullpost"> tapi sebelum kode </span>.

Untuk artikel yang pendek, korang tinggal buang je kode tadi tu.. selesai.
Kalau x tau jugak.. call jer aku...
Ok... selamat mencuba...
Wassalam!

JEBAT DRAG RACE

2009-07-31T15:28:00.002+08:00

ROSSI 2008

2009-07-31T09:25:00.000+08:00