1990 YZ250

[tsuruca]

Anybody gotta 1990 YZ250 that didnt respond to idle adjustments at the carb?
It will idle slowly, by itself for about 5 seconds warm (does not fast idle and drop like an intake leak). Stuff I did: brand new stock carb, replace reeds (stock), silencer is repacked, filter clean, exhaust power valve is rebuilt and operational, main is 2 sizes larger (370), has a pro circuit pipe, stock pilot jet 45 (tried 40), one size slimmer needle, middle pos. (was hesitating), plug chop is black dry, likes air mix screw out approx. 1 1/2-2, timing is on, compression checks to 150 lbs. , tried larger cut out sizes on slide-no luck. This bike runs GREAT and strong except the darn idle problem. Anybody had any similar problems? Is this a ignition problem?:
Jetted up, jetted down. No effect on the idle.

[offroad101]

mine is an 89 WR.

I was having problems with mine idleing also....after five or seconds at idle, it would die out. Tried adjusting the idle adjustment, no help. Had the carb cleaned by my mechanic (never cleaned this one before to that point), and he said it had a lot of junk in it.

The bike had sat for a few years in a buddies basement, but when he rode it, he liked the more wide open trails in Michigan vs the more technical ones I like to to ride in Mo. Anyway, the bike scremed also, but after cleaning the carb, I was fouling plugs badly on my last trip to Mo.

I have not been able to ride it on a trip, but took it out for a test run here in IL around the farm. The only bad thing is it was fairly cold, 32 degrees or so. But it idles nicely.

It had a 380 main jet in it before, but the needle was on number 5 (putting needle all the way up) and a pilot of 50 (not stock). I put the carb back to completely stock settings except for the pilot jet and air screw.

Needle # Same # 3 neutral (standard)
Main # 340 (standard)
Pilot # 50 - larger than stock
Air Screw – 1 turn out (1.5 stock)

Like I said the bike idles now, but in a colder environment then I usually ride. But I will say this, I did not notice a loss of power, but actually thought in had more mid to low power than before.
hope this helps,
Ryan

[tsuruca]

I have one that did the same thing. I tried everything! I ended up calling eric gor at his shop. Apperantly mikuni tmx carbs do not have an idle circuit. I had also bought a new one of those a while back too! (darn). So they are not really designed for a sustained idle. Check out yours. No choke circuit with idle adjust. Just a screw that hold up the slide. Anyways, I ended up getting a keihin carb from sudco. Works awesomesome now! They also have the jetting spec for most pipe combo's. I slaved over this bike for over a year and replaced or adjusted almost everything. Now I wouldn't part with it for sentimental reasons! Haha

[yamahor]

haha, yes. I have 93yz, bought it an was pissed off, thought somthing was screwed
but it was the old mikuni's

[bitshifter]

Tsuruca, Do you know what keihin carb you have now? I have an 89 with the same problem and I think I would like to try your solution. Was it a bolt on or did you need a different cable etc?
Thanks