my 400's got me doun

[1fst400]

today at the track it seemed as tho my 400 was constantly dogging out. low on power. and missfiring on top end.

I suck at jetting. Im running a fcr carb, im running a 175 main. time to go bigger on the main. hasent been running right scence I installed a higer comp piston.

[Ex'r Marlin]

Question:

Are you running a stock exhaust?

If so, try running your atv without the airbox lid and see if that makes a noticeable improvement.

If that makes an improvement, and/or you need it to improve even more, you most likely will need to go with at least an aftermarket slip-on exhaust to allow more air flow through.

Note: Once I went to a higher compression piston (10.8 to 1), it did not matter what jets I put in it... The atv ran terrible until I put a slip-on exhaust on it. BINGO... Problem solved.

Best wishes with your first atv!:macho Congrats on getting a HONDA!:D

[EXevan91]

what is the comp ratio on the piston u installed ?

[1fst400]

12:1 je piston. and everything eltse, 416 bore

[CHEVYZ]

What kind of fuel are you running?

[1fst400]

vp red.

the answer Im after is does missfiring on top end come from bad jetting or is my problem eltseware.

[CHEVYZ]

Try rejetting with a little bit larger on the main and see if it helps any. You may have to play with the tune for a little while to get it just right. Misfiring on the top is an indication in most cases of being a little lean.