300ex help!

[SteveRidesQuads]

i have a 300ex with a built motor, 400ex carb, and cid blah blah blah...

so it runs fine when its cold, revs perfect runs fine. but when it heats up it just doesnt run right. ill be riding and it will just loose power then start up again like on off on off on off all by itsself with me holding the throttle wide open.

any ideas of what is wrong? please help.

[bwamos]

Are the rev's bouncing? At a fairly low rpm like 4k?

If so you just have a poor contact/ground at the reverse indicator switch under the rear brake pedal, or in the wire harness connector.

Just throwing out the easy one to start with.

[SteveRidesQuads]

no i dont think so, but heres the thing. I went up to a track (mile mountain) for a race a week ago and had to lean out the carb due to elevation changes, im going to richen it back up and see if it makes a difference.

[TRX-330]

I have the same problem with mine. It runs like a champ when cool but when it warms up runs like crap it like gives out, looses power then re-gains it. I know im not jetted perfect yet so that might be the problem with mine too. I think i am running to lean still. Lean=white spark plug and rich=black spark plug Right? or do i have them mixed up?

[bwamos]

Yes and no.

YOu can't just pull the spark plug and look. That's a poor indicator.

You have to do a "run". Ride it at the desired rpm for a bit, then while maintiaining the throttle hit the kill switch and keep holding the throttle until the engine stops.

Do a search on plug chop technique.

Or, you could cheat like me and take it to a dyno for an A/F run.. LOL.

[Redhotrod]

Originally posted by bwamos
Are the rev's bouncing? At a fairly low rpm like 4k?

If so you just have a poor contact/ground at the reverse indicator switch under the rear brake pedal, or in the wire harness connector.

Just throwing out the easy one to start with.

Wow, this saved me a trip to the dealer, My connector was broke for a while I believe and finally lost all connection today and the bike would not even start! took off the black metal cover to find the 2 wires behind the foot brake and 1 was just hanging off in there.
Bike use to do the same crap, acting like hitting a rev limiter at half throttle, I was playing with jetting but having a hell of a time fighting a rev limiter to get the main jetting right. I will have to double check it now again. But the bike runs awesome now, just gotta retune.