Dirt Bike Carb Question

[ddragon63]

OK Fella's I'm scratching my head over this one....

My 2000 XR400R is pissing me off!

Fires right up, runs great! BUT!!!! The idle is erratic

I've checked for vacuum leaks, I've adjusted the push pull cables. The throttle comes back down onto the idle screw every time. Choke butterfly stays put. But it likes to stick a high idle, which takes a few raps of the throttle to get it back down. It seems to have 3 stages.... normal, a little high, and holy CRAP come back down!

Any ideas? Other than pull carb, dismantle, clean and reassemble I can't think of anything else. I've got to be missing something!

[XJfan1]

I had bought a 2003 honda xr80 for my son. Once again the po was a real smart one and it say about 3 years with gas in it. I cleaned the carb and tank oil change a a few other things it did the same thing you are talking about the idle was all over the place for no real reason. I pulled my carb back off and found a bad intake gasket between the carb and the head and there was a chunk of crap in the primary jet. New gasket and cleaned the carb and she purrs like a kitten

[ddragon63]

I had bought a 2003 honda xr80 for my son. Once again the po was a real smart one and it say about 3 years with gas in it. I cleaned the carb and tank oil change a a few other things it did the same thing you are talking about the idle was all over the place for no real reason. I pulled my carb back off and found a bad intake gasket between the carb and the head and there was a chunk of crap in the primary jet. New gasket and cleaned the carb and she purrs like a kitten

Ya I'm thinkin i got something floating around in there partially blocking a jet every now and then causing a leaning effect. once I burp the throttle a few times it probably stirs it around. The carb is in a boot/holder not attached directly to the head.

So I guess we tear the carb apart before I kick it off the lift and walk away

Tomorrow is another day. I'll let it think about what it has done

[natemoen]

Try richening the idle mix some. If idle is too lean it can.cause the idle to hang up some.

[ddragon63]

Try richening the idle mix some. If idle is too lean it can.cause the idle to hang up some.

I'll give that a try Nate

[Lonerider62]

Whenever you have a problem that indicates a fueling issue, it's always a good idea to check all gaskets (and there has to be one somewhere between the carb and the head) and a good carb cleaning is just a part of the problem solving proceedure. I'd check the air cleaner/replace too.

[ddragon63]

Whenever you have a problem that indicates a fueling issue, it's always a good idea to check all gaskets (and there has to be one somewhere between the carb and the head) and a good carb cleaning is just a part of the problem solving proceedure. I'd check the air cleaner/replace too.

It does it whether the air cleaner is in or not. I sprayed the intake down with startig fluid, no idle change. I'm gonna assume @ this point my flushing of the carb wasn't good enough and it wants its bowl removed, jets and tubes cleaned, and put back together.

[trbig]

Try richening the idle mix some. If idle is too lean it can.cause the idle to hang up some.

+1. My son's was doing the same thing. Just idling, the exhaust would glow bright red. I turned the idle mixture screw way way out, and it does much better and idles at a way cooler temp. Blipping the trottle also returns to a normal idle now.

It doesn't make sense, but a lean condition does make the idle go up. Much like running out of gas on the lawn mower or chainsaw, when it's about to run out it idles way way up and won't come down until it's completely out.

[ddragon63]

+1. My son's was doing the same thing. Just idling, the exhaust would glow bright red. I turned the idle mixture screw way way out, and it does much better and idles at a way cooler temp. Blipping the trottle also returns to a normal idle now.

It doesn't make sense, but a lean condition does make the idle go up. Much like running out of gas on the lawn mower or chainsaw, when it's about to run out it idles way way up and won't come down until it's completely out.

I'll give it a shot tonight when I get home. Thanks for the help fella's

[ddragon63]

Ok fella's here's where I'm at.

I opened the mixture screw up a ton... No change. I sprayed everything down with seafoam... No vac leaks. I took the carb out a dismantled. Looked pretty clean but i pulled the jets out and blew seafoam and air thru everything and put it back together. Still doing it.
So while the tail piece and air box was off I investigated the slide. I got it down to its normal idle and found and Allen key just too big to fit under the slide. If I forced it in it would rev up. I blurped the throttle till it stuck up high. Same Allen key fits cleanly under slide. So I'm gonna go ahead and say the slide is sticking.

Now with that said my automotive carb knowledge is vast... But my motorcycle carb knowledge is not so well.

How so it fix a sticky slide? thanks in advance and you have full permission to laugh at me right now

[ddragon63]

by my findings I'm going to assume either the needle is hanging on the main jet or there is some crap between the slide and the carb body making it stick. or a gummed up armature. I guess I need to pull it all apart and clean real well and verify everything is operating normal before re-installation. it came back onto the idle screw every time i flopped it.

[ddragon63]

I WIN!

I took the carb apart, again and took the slide fully out and the neddle fully out. someone had it set @ the very top notch.... So I put it back in the middle where it is suppose to be stock and TA-DAH!!! its not perfect but its alot better now

[natemoen]

Just moving the needle stopped it from hanging up?

[ddragon63]

it seems so... still got stock jets in it. I should jet it up a little with the pro circuit pipe. We'll see how it plays out. I could probably stand to move the needle another stop up to fatten it a bit.