'90 YZ 250 (Mikuni question)

Joined
Apr 24, 2003
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#1
And there's no external adjustment to fix it... Just one external screw and that seems to adjust idle mixture or something...
The carb on my bike doesnt look like the ones in my clymer manual, they have external idle adjustments, like the keihin on my KX that I'm used to.
Note: There's one other external adjustment on mine, a "throttle stop" screw with an 8mm lock nut. This doesnt seem to lower my high-ass idle.
btw, the reeds were fine, just put em back in, top end is fresh with new bore + hone.

-if anyone has experience with this carb or this bike, I'd appreciate any input greatly!!!
thanks, alex
 
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Apr 24, 2003
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#2
My plug was very clean and just wet after this, must be too lean...
could an air leak be to blame? I hope the lean, high idle didnt hurt my new top end.

thanks for any info!! -alex
 
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Dec 9, 2002
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#3
Did he bike idle high before you did the top end? If not I'd look for a air leak in the intake... and at the base of the jug. Use a spray of liquid around any potential leaking area with the bike running... any change in the RMP's indicates a leak. I like DW 40 or some people use carb or contact cleaner.. I like WD because it will not strip the oils from a already lean cylinder. Also some of the carb's incorporated the idle and the choke on the same knob. I'm not sure if yours is but you could give it a turn and see it if is. Also maybe there is some trash in the carb hanging up the needle.. just a thought.
 
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#4
before i did the top end, it idled high when cold but when warm the idle would lower so far that it wouldnt idle without throttle blips. Now it just idles real real high.
i'm thinking its either an air leak or carb issue...
btw, should the throttle slide sit all the way closed in this carb when throttle twist is in idle position?

thanks, alex