Where is the best setting for the 2 air/ fuel screws?

The H and L screws are both fuel screws, opening them richens the mixture, base settings are usually one turn open from closed on both, the L screw will ajust the mixture at idle and up to half throttle,if the saw does not pick up smoothly richen this screw a bit at a time the H screw will ajust the mixture from half throttle to max throttle, just remember the H screw is more than capable of increaseing the max engine speed to the point where it will seize, most hobby saws run at approx 12000 rpm, you must have a means of checking the max rpm ( tacho ) before any adjustment of the H screws is attempted. Always remember you should not adjust the carb to compensate for other fuel related problems ( fuel blockages )

Husqvarna man
January 2010