Tune Carby for small two cycle engine in brushcutter


Old 01-27-08, 10:15 PM
ozriverboy's Avatar
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Tune Carby for small two cycle engine in brushcutter

I have a 30cc brushcutter and had to replace the carby with a similar carby which works rather well except I need to tune it. I notice that there are two adjustment screws for the carby, one marked 'H' and the other 'L' which I take to mean 'high revs' and 'low revs' respectively. What exactly do I do to tune the carby so that the engine runs smoothly and efficiently with respect to the two adjustables and the idler adjuster.
Regards to all.
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Old 01-28-08, 12:56 AM
repair_guy's Avatar
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Location: Marion,Al.
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Yes your right in thinking that the "H" is for high and the "L" is for low rev's.and the other screw is for idle.Take the screws with "H" and "L" on them and turn them all the way in,CW.DON'T TIGHTEN just bottom out.Then turn both screws out CCW 1-1/2 turns.Crank the engine an let it warm up.(2 or 3 min.)Then while hands off the trigger fine-tune the screw that says "L".Then with trigger mashed fine-tune the screw that says "H".If it's ideling too fast or slow then adjust the idle screw.in=faster.out=slower.TURN SCREWS SLOWLY.
Old 01-28-08, 09:40 PM
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Be careful when adjusting them so that you don't get it running too lean. If you adjust the high speed mixture screw to the point where the engine runs the fastest and smoothest, it will ruin the engine, because it is too lean at that point. You'll want to find that point, and then open the screw a little more until the engine gets a little flutter sound at full throttle. Adjust the low speed mixture screw to the best idle attainable and just rich enough that there is a nice transition from idle to full throttle, no stumble in between.

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