I have never jetted a 4-stroke before and was wondering how to go about it. How can you tell if you are too rich or too lean? What are the procedures on jetting for the idle jet, needle, and main jet? And finally, do you have to re-jet when changing pipes?


First of all your spark plug should be white to light brown. If its sooty, you're too rich.

If you put a more liberated exhaust, you might run a little richer.

But I would say that rejetting is not the right word.

First you have to describe the symptoms, what's wrong or what you don't like in the jetting behaviour. For example engine dieing when wacking the throttle, or a hesitating spot ...

Anything that effects the fuel/air mixure can effect jetting.

Less restrictive pipes allow the engine to pump more air...more air requires more fuel... Changing to a less restrictive pipes (alone) tend to LEAN out a bike. (more air pumped through the engine). Most pipe makers provide a jetting spec with there pipes as a starting point..

As far as "how to jet" that's been covered here a bunch before... search on "jetting" you'll see what I mean... :)

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