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david857

01 Yz 426 No More Fouled Plugs

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If anyone else is having trouble fouling plugs on the 426 I have found the solution that may work for you. First I changed the plug to an NGK CR7E. Second was I always turn off the gas and let it run for a couple minutes periodically reving it to burn off the excess gas. Third but not least is NEVER EVER EVER no matter what DO NOT give it gas while trying to start it. These simple steps have helped me have the same plug for a month where I use to change it every ride.

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the CR7E is TOO HOT to run in the 426. As a matter of fact I ran CR9E plugs in my 426 for three years. The heat range of the plug is not the problem with fouling. However running a plug that hot will/could cause a lot of damage to your motor. The 426 does not need any help running hotter! LOL

Proper jetting, proper starting procedure and a clean carb will end your fouling problems.

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Sounds like your jetting maybe a bit rich. What are your specs? 426's should run on CR8E's without fouling. By running your bike out of gas you are leaning it out and drying your plug for the next start up, which is okay, but not necessary when carborated correctly.

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The term "heat range" refers to the relative temperature of the core nose of a spark plug. The words "hot" or "cold," when used in referencing spark plugs, are often a source of confusion and misunderstanding, since normally a hot spark plug is used in a cold engine (low horsepower ) and a cold plug in a hot engine (high horsepower). The terms actually refer to the heat rating or thermal characteristics of the plug; more specifically, the plug's ability to dissipate heat from its firing end into the engine cooling system. A cold plug transfers heat rapidly away from its firing end into the cooling system and is used to avoid core nose heat saturation where combustion chamber or cylinder head temperatures are relatively high. A hot spark plug has a much slower rate of heat transfer and is used to avoid fouling where combustion chamber or cylinder head temperatures are relatively low. The primary means of adjusting heat range are by varying the length of the core nose and the alloy material used in the electrodes. Hot plugs have a relatively long insulator nose with a long heat transfer path. Cold plugs have a much shorter insulator nose and thus, transfer heat more rapidly (see illustration; hot to cold - left to right). The heat range of a plug does not affect the power output of an engine. Rather, it allows the plug to function as designed for the duration of the racing event. In other words, once the correct heat range is found that prevents fouling and does not contribute to the pre-ignition or detonation, a change to a hotter or colder plug will not have a positive effect on engine performance.

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, once the correct heat range is found that prevents fouling and does not contribute to the pre-ignition or detonation, a change to a hotter or colder plug will not have a positive effect on engine performance.

Exactly....and that is where the problems start.

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