Also make sure that the engine is fully warmed up. The "L" mixture screw should be set first, as it will feed some fuel to the engine at high speeds and effect the final setting of the "H" screw.
When setting the "L" screw, find the leanest setting that provides the highest possible idle rpms, then go counterclockwise or rich until you just hear the engine slow ever so slightly. This will be very close to the final setting. The "L" screw not only provides idle fuel, but it feeds fuel to the engine to help get it thru transition to full throttle. A lean "L" setting may provide a smooth/clean idle, but more often than not the engine will hesitate or even stall out when the throttle is quickly moved to wide open.
The idea here is to find the leanes setting the for the "L" screw that the saw will tolerate so it still accellerates smooth/clean and doesn't hesitate, bog, etc. Going too rich will get rid of any hesitation/bog, but can cause the engine to stall or load up at idle speed.
For a new P/C it is a good idea to add some extra oil mix and set the "H" screw just a tad rich as well. This lets the engine avoid really high rpm's during break-in and provides it with plenty of lubrication.
Once you have ran several tanks of fuel through it, set the "H" screw for best power in the cut without going lean. Basically, anytime during the cut the load is removed, the engine should start "4 stroking" just above the best rpm's it prefers in the cut.
Some folks simply try to achieve the highest possible rpm's from the engine at no load, then at full power in the cut the saw sees a lean condition, and smokes the P/C.
Basically, it is better to have the engine run slightly slower at full throttle, with a rich mixture. This will provide improved lubrication to the all the parts, and avoids really high EGT's, both of which are a death sentence for the engine if/when the EGT's get really high and lubrication is minimal. Hope this helps some?.....Cliff
PS: also be aware that the saws ideal A/F ratio can change slightly once the new P/C is fully seated in. Weather and D/A (Density/Altitude) are also a contributing factor to the precise or ideal "H" speed setting(s). This changes throughout the year, so be prepared to adjust the carburetor accordingly.
