poulan chainsaw carburetor adjustments?

other than setting ideal speed, how would i go about adjusting the carb to run smooth at ideal speed and run underload at top speed? again providing everything is clean and good. have purchased 4 new saws and after they run for 5 mins. they have issuse with carb adjustments. also where does one get the special screw driver to adjust with?? there must be a set way going about setting these carbs up.....
poulan 2150, 4200, 4600 series