Simple 2002 YZ250 Jetting Question

[Lubeboy]

I have heard mixed answers to a basic question...

Started off with stock... added FMF pipe and Rad Valve.

In general, should main and pilot jetting get bigger or smaller.

I hear that stock jetting is very conservative, so with improvements, you should put smaller jets?

I have also hear, with the mods, more air flow requires more fuel, so you should put larger jets?

Thanks for any advice.. :coocoo:

 

[Lubeboy]

Nobody has an opinion on this? Please please?

 

[i_955]

Yo,

Jetting is so subjective to environmental conditions that only you can determine the bikes performance on any given day/ride. What is prefect during a brisk early morning ride becomes boggy, unresponsive when the afternoon sun heats and moistens the air, or you climbed several hundred feet.
The YZ manual has a very impressive section on tuning. Read it, study it, know it. Take notes, jets & needles with you and understanding what the bike is telling you is the only way you'll tune it.

Assuming you know this already, I've simply been typing for all this for finger exercise. There is a thread at the top of the 2 stroke section with huge amounts of info on jetting
http://dirtrider.net/forums3/showthread.php?t=42618
and I believe it was there that I read that yes, adding a Rad Valve often required the carb to be jetted leaner in one or more circuits. This is again assuming that your bike is running properly before the mods. If it was running lean before the mods, then you do the mods & lean the jetting before the test ride the motor could sieze.

The KX manuals also have a great jetting section.

Chow