400ex cutting out in topend

[Grant Casey]

here is my story,,, my bike hamers till it gets to up op rev's then it just starts to break down and not go any were, like u pin it threw 1st 2nd, when i get 2 3rd and hold it flat it stuffs up and dies same as 4th 5th it only dose it in topend but,


i thought it was a clogged carb but i cleaned the carb and nothin was wrong, there r no air leaks in the carb boots... only thing i can think of now is the CDI

[QuadManiac]

Noticing all the mods, especially the 450 carb. Did this ever run right with the mods or has it always had this problem? If always, i'd say your main jet is wrong.

Does the prob follow RPM or throttle position? If it's throttle position, it's likely the jet (or needle position), if RPM it's elsewhere.

Good Luck!

[Grant Casey]

it was runnig fine 4 like 6 hours then it stuffed up

[QuadManiac]

And as to the other question - throttle or RPM?

What's your air filter look like?

Also, not very likely, but has happened: At higher RPM's and heat marginal insulation in the coil and spark plug wire can break down and allow HV to short outside the wire... try revving it in the dark, if possible, and see if there are any sparks flying.

[Grant Casey]

well i hold it full noise 4 abit then it stuffs up,, its rpm

the air filter is good


i will try check that coil thing, the coil is fairly new only 2 months old

[QuadManiac]

How long's a bit? You may be running your float bowl empty. Make sure the float is set high enough, the tank outlet and petcock are free flowing and there's no other restrictions in the fuel flow to the carb, like a plugged external fuel filter?

[Grant Casey]

yeah i cleaned the carb, but i might do it again , the only place were i think it might b cloged is were the fuel gose in............but my mate told me it dosent sound like its starving of fuel

[QuadManiac]

If you always listen to mates, you may never find the problem! ;-}

[Grant Casey]

but yeah wheni get free time tomorow ill pull that carb down

[zrpilot]

could you be hitting the rev limiter?

[Grant Casey]

na its not hitting the rev limiter