Sputtering, breaking up at WOT at high rpms.

[Grahxen]

I have a 2007 400ex with a lexx slip on, uni air filter, 155 main jet and a 40 pilot. I have been noticing now that I can finally open it up that at WOT, especially notice it in 1st and 2nd where i can really rev it that it starts to break up, sputter. Usually if my mechanics background is correct this is a sign of lack of fuel. My question is isnt a 155 main jet more then enough for the slip on and uni filter? Air box lid isnt open either. Quad still has the same amount of power, runs fine except for the breaking up at high rpms and wot. It is also not the rpm limiter kicking in. I would like some input before i start rejetting it. Ive changed the plug and also checked my valves as well.

Thanks for any help.

[BigBore24]

what did the plug look like? just bump up to a 160 and see what happens. it only takes 5 minutes to try and if its no better then youve got another issue

[Grahxen]

Old plug i took out seemed to be normally colored, tan definatly not black. And also i did notice the problem after i rejetted and put the pipe and air filter on. I had a 152 main in there prior and the 155 i thought made it a bit better. What does it sound like when you hit the rev limiter? The sound i hear is basically the engine breaking up, popping and possibly even a backfire sound which is why i suggested running to lean.

[BigBore24]

you need to really determine if the problem is based on the position of the throttle (half throttle or wide open) or if its based on your level of rpms. even with a stock cdi hitting the rev limiter on an ex is pretty rare considering the power drops off before you get to the limiter. id start with jetting. you may just have to keep messing with it until you get it right

[Grahxen]

its only wot at high rpms, i can be WOT at lower rpms and it is fine, it is only when i am reaching high rpms at wot where it breaks up.

[BigBore24]

could be electrical then. ive heard of stators causing this, but you really need to do some good diagnosing or have someone else do it. i dont want to tell you to start buying parts and throwing them on there if you know what i mean.

[BigBore24]

where you from?

[Grahxen]

NJ