engine starting to break up at

[zzbudzz]

high rpm's . i have a '02 400ex when i have the engine's rpm's up it starts to break just a little bit. do i have a air leak ,bad spark plug? i haven't really looked at it real close yet, just trying to find out where to start looking?

[AtvMxRider]

What size jet are you running?

[zzbudzz]

155 i believe ? it just started doing it? i had the jet in for over a year now.......could it be bad gas? probably something dumb and simple:rolleyes:

[Ryan]

Check your piston rings.

[JOEX]

I'd replace the plug first.:)

Joe

[AtvMxRider]

Originally posted by Ryan
Check your piston rings.


It's not that. I would try changing the plug Buddy. You should also try cleaning the carb.

[A.K.A Nips]

I had the same problem last summer, it was a loose ground off of my kill switch. it would only do it at high rpms becouse of the vibration. so check all your grounds.

[AtvMxRider]

Originally posted by A.K.A Nips
I had the same problem last summer, it was a loose ground off of my kill switch. it would only do it at high rpms becouse of the vibration. so check all your grounds.

Hey Buddy I didn't think of that. You did have the plastic off. Check the wire going to the frame.

[NTPRacing#19]

if your running a slightly biger jet with a completly stock motor and stock exhuast and all then it just might be simply flooding itself out with tio much fuel. and if your plug is a dark charcol color you are running it way to rich, they plug should look like a grey chalk color when its jetted right

[AtvMxRider]

He's running a E-Series and a K&N. I think the loose ground is his problem cause he had the plastic off and it ran fine before that.

[sparks400]

my friends did the same thing sunday and all he did was change the plug and thats it.

[zzbudzz]

i cleaned the plug , it seems to run alot better. i think i'm running too rich cause my plug is dark colored. i'm going to get a new plug today and try that. i have e series with 160 main ,42 pilot jet,choke removed and , needle clip down one notch.i think i nee to goto a smaller main jet.....

[cals400ex]

i would try to put the needle back in the stock position and turn the fuel skrew out a little more. i did this with good success, but i run a 45 pilot. i would be running a 155 main if you have a K&N. do you have a K&N also? without the K&N i would put in a 152.

[zzbudzz]

yeah, i got a k &n filter. so, try and turn the fuel screw OUT how much? 1/4 turn 1/2 turn?

[AtvMxRider]

Originally posted by zzbudzz
i cleaned the plug , it seems to run alot better. i think i'm running too rich cause my plug is dark colored. i'm going to get a new plug today and try that. i have e series with 160 main ,42 pilot jet,choke removed and , needle clip down one notch.i think i nee to goto a smaller main jet.....


Hmmmmm I'm running the same and mine is ok. Just try changing the plug Roscoe.

[cals400ex]

i would run a 155 keihin main jet. your 42 pilot would be just fine. i would try 2.5 or 3 turns out on the fuel skrew if you put your needle in the stock position(3rd position). if you leave your needle in the 4th position, you probally won't be able to come out 3 turns or you will be overly rich. i had better luck starting the bike when i put the needle back in the stock position and just turned the fuel skrew out more. when i had the needle in the 4th positon it was running a bit rich when giving the bike little amounts of throttle. it was still hard to start then too.