i need help with a miss

[killer454]

i have a 400ex 2000 and i just put a new intake manifold on it and rejeted the carb.The carb is runing real good throttle response is perfect,wot is good.

my problem is this:when the engine is at idle it idles fine for 15-20 seconds then it misses one time then idles perfect for about 15-30 seconds and does it again.

this is just a slight miss i dont understand it,this atv is running real good just the miss at idle.

atv has these mods and jets now:
.020 11-1 piston
hotcams stage 1
no lid
uni filter
stock header
pro-circuit t-4 pipe

i just rejeted today and installed a new intake on this atv,here is the jetting:
pilot 38
main 170
needle on 4th slot down
i pulled the plug after the test ride and the plug was a cardboard color (tan)so i think i right on on the jetting.

can anybody tell me what to look at on this funny miss every 15-20-30 seconds?
it only has this one miss at idle if you rev the moter to 2000 rpms it does not miss at all.

i have checked all wireing and grounds

[rubbersdown]

If it runs fine at every portion of throttle but only has a skip at idle every 30 sec. dont even worry about it. Just ride it. ntn you can do.

[killer454]

ya i am riding it but just wanna know if it can be fixed.

[MtnEX]

Let it set at idle til it misses.

Then while in neutral, slowly start to give it steady throttle... add a little more... add a little more...

See if it acts up like that with no load on the engine.

[killer454]

yes i have done that it does the same thing.it seems like a miss at the plug but it only happens once every 10-15 seconds.the atv runs excelent.but has this slight miss when at idle,and in neutral when i give it gas.if it has a load on the engine with the atv in gear it runs excellent.i have climbed big hills with it and while going up the hills no miss.

[CJM]

Sure plug is gapped right. Stupid as it sounds it is possible.

Check the plug for any hairline cracks or such too.

[MtnEX]

Originally posted by killer454
yes i have done that it does the same thing.it seems like a miss at the plug but it only happens once every 10-15 seconds.the atv runs excelent.but has this slight miss when at idle,and in neutral when i give it gas.if it has a load on the engine with the atv in gear it runs excellent.i have climbed big hills with it and while going up the hills no miss.

Same problem here with a fuel injected machine...

Check your intake for leaks... I mean every bit of it... every connection, and spray the whole thing with something while it is idling... even the booty and stuff between the carb and head.

If that is not it, get a new exhaust gasket and try that. My friend swears this is my problem...

We shall find out...

Please let me know what happens.
I know how frustrating this is...