Aug 1, 2000
I am a novice who is trying to figure out this jetting thing. I have an '01 RM250 which ran great (maybe a little rich) but did not idle.
A guy at the track re-jetted it and it will idle fine, but now it is not as crisp off the bottom. Did I read where Keihin carbs run better when adjusted not to idle. Is it possible for me to have idle AND good 1/3 throttle response?


Mod Ban
Dec 10, 2000
You just need to do a little fine tuning of your pilot circuit. When the bike is at operating temperature, adjust the air-screw until you find the highest idle. If you are less than 1 turn from fully closed, you need a larger pilot jet. If you are more than 2.5 turns out, you need a smaller pilot jet. Once you have determined the correct pilot jet size, find the highest idle point, set the idle speed so that the engine barely idles, then ride it. Make small adjustments in both directions with the air screw until you find the point that gives you the best response when snapping the throttle open. My bike is sensitive to less than 1/8 turn adjustments. Remember, this setting will change as the temperature and humidity changes, it is not a set-it-and-leave-it adjustment.
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