High is 7/8 ths of a turn out from lightly seated. Low would be 1-1/4 turn out. This is ball park settings. The saw should run but will need fine tuning. Be careful not to turn the H screw in to far and lean out the mixture and damage the motor.
The idle adjustment should rest, centered on the pointed end of the idle speed adj. screw. Once the H and L jets are adjusted then you want to turn the idle screw out as far as possible so the idle is set at the lowest smootly running speed you can achieve.
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If it has contact breakers and a condensor, check that the contact foot that rides the timing cam, is not worn down. Check the contact gap and the contact faces for pits and spikes. The faces should be flat, clean and smooth. The gap should be as per the owners handbook/ motor spec plate. Check for spark at HT lead plug cap before checking plug for spark.
It is likely the choke shutter. Stihl apparently had two issues with this design: one is that the original air filters had a rubber gasket instead of the hard nylon ring; if yours is that version, and you bought a replacement filter with the white plastic ring that goes over the carberuter throat, you may need to update your choke shutter and/or just replace the cover. The other choke-related issue is that the cover sometimes warps, causing the choke shutter to not seat properly. Stihl made another style of cover that moves the choke shutter up and down instead of side to side, and I suspect it was to address this problem. If you want to check, try taking the cover off, plugging the throat of the carb with your thumb, and starting it. If it starts, you just confirmed your choke problem.