jetting

[tom73cuda]

I have a 2002 400ex with a full white brothers exhaust and open k&n filter.a 42 pilot and a 155 main. at idle it has a slight mis. then when you give it gas it pops out the pipe with black smoke could this be jetting or a cdi problem or do i make no sense

[Honda#4]

go up to a 160 and try turning your idle up a bit that mite help.

For me i had a white bros pipe and no air box and k&n filter and i needed to go t oa 165 main. Dont for get to adj the needle cause when you take off the air box lid and change filters thats dealing mainly with the needle which deals with half throttle.

[Wheelie]

The main jet is fine, step down one size on the pilot.

[jsmith2232]

Main should be fine, the pilot might be a bit on the big size you could probably turn your fuel screw in a bit and see if that helps.

[zrpilot]

Originally posted by LTD
For me i had a white bros pipe and no air box and k&n filter and i needed to go t oa 165 main. Dont for get to adj the needle cause when you take off the air box lid and change filters thats dealing mainly with the needle which deals with half throttle.

Yep me too!:D

Based on the advice of a VERY knowledgeable engine builder, I also ran a 170 main and I think it actually ran better.