Chainsaw tuning: H, L and LA screws without a tach, and when to stop

Start with the factory base settings (usually 1 turn out each, check the manual). Warm it up. L (low): turn in until it stumbles, out until it burbles, split the difference, then a hair rich. LA (idle): chain must not move at idle; set just above the clutch engagement point. H (high): at full throttle, turn in until it screams clean, then back out until it just starts to four-stroke (a burbling, "blubbering" sound) off-load. That four-stroking is the safe setting; a saw that screams clean at WOT with no load is lean and will score the piston.

If you cannot get it to tune, you have an air leak (crank seals, intake boot) or a plugged fuel filter, not a carb setting problem.