I have an 86 TRX250R and I'm having trouble with fouling plugs. My machine has some port work, factory carb, fmf fatty pipe with K&N filter and boyseen reeds and is bored 30 over. I am running a 42 pilot jet and a 147 main with the needle in the third groove. The air screw is turned all the way out. I am run a 32:1 mixture. It has a hard time idling but runs well off the idle. I foul a plug with every tankful. I've checked the plug after a run and it coco brown so I think the main jettig is ok even though you would think that I should be running a bigger main. I am a sea level.

Some questions, does turning the airscrew out lean out the idle/lowend mixture.

Does a bigger pilot jet rich the mixture and will this help it idle, will it make the fouling worse?

Does putting the clip on a lower groove in the needle richer or lean the idle mixture?

Any help would be appreiciated.

 

Turning the airscrew in will richen the mixture slightly. It is to fine tune the pilot jet. A larger pilot will richen the mixture also.

By raising the needle/lowering the clip, you are letting more fuel in which also makes it more rich.

Your jetting seems very low across the board. With a K&N filter and pipe you should be running richer than that even at sea level. Is your airbox still on? Check your wiring for loose connections or broken wires.
ERIC

 

The airbox cover is off, I can't figure it. I would expect it to be lean if anything.

Are the stock jets 150 main and 50 pilot?

Maybe I should start with the stock setting and work fro there.

 

Any one else?

 

I believe the stock pilot is a 48, that is probably your idling problem, that and the air screw should usually be 1-2 turns out, more specifically 1.5-2. My pilot is a 48 with about 1.75 turns out on the air screw. Dave