been thru many of the same engine problems that you describe and it seems that when the engine has been run hot, it tends to want to stall after you get it running again... air leaks would show up as a lean condition... try leaving the low speed needle flush and work more off the high speed... again.. you will have to experiment as to which way to go... also, for the idle, try to raise the idle speed on the carb to just below when the clutch engages... it will allow the engine to run without stalling as much....