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lawdog

High-Low Idle carbs

4 posts in this topic

You know the ones, they are on these little engines like weed eaters and such, they have a low idle screw and a high idle screw. How do you set these? I've never really messed with them.

I have one that won't idle, but if I put the choke on a little then it will keep running. When I go back to full throttle it will run OK but with the choke slightly on like that it gets pretty rich. Where should I start on adjustments????

thanks.

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Most likely the carb is dirty, and will need to be cleaned.

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Having to choke to run means your running lean.

Start with the low speed adjustment. If you like turn the screw in till it just makes contact, NOT TIGHT. As you do this count the turns. Now turn counterclockwise(out) back to where you started. Start up the trimmer and and make small 1/8th turn and slow adjustments counterclockwise. Do this till the trimmer will idle without choke.

Do the same steps to get your starting point for the High speed adjustment.

Start the trimmer, turn the screw out with small and slow adjustments with full throttle while under load(trimmer string should be enough) till the trimmer runs without choke. Go back and fine tune the idle by turning in till it just starts to idle at a high RPM then back out a hair.

Now go back and fine tune the High speed. Turn in while at full throtle till the RPMs increase, then back it back out a hair.

Now if you don't notice any change while adjusting idle or high speed its time to clean the carb.

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(probably stating the obvious) There are two prerequisites I would add to Franks otherwise proper method of fine tuning a small two stroke.....

Before starting to make adjustments, make sure the air cleaner is clean and the motor is fully warmed up. Most of these small two strokes are pretty sensitive to small adjustments and temperature change.

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