Here"s my H carb adjusting procedure, put together by combining 3 or 4 different manuals;
Make sure the float isnít sticking or touching the insides of the float chamber. Some previous advice was to use a Dremel tool and smooth the insides of the float chamber so it doesnít rub or touch. Pretty important. Set the float so the top of it rests 1 27/32" above the flat surface of the float chamber. Initial settings are as follows to get it started;
Main fuel adjusting screw, big screw facing down at an angle, towards the rear, at the bottom of the carb; 2 1/2 to 3 turns open. This main screw turns clock-wise for leaner mixture. [This screw adjusts fuel.]
Idle air-mixture screw, smaller screw facing forwards, on upper left-hand side of carb; 1 to 1 1/2 turns open. This idle screw turns counter-clockwise for leaner. [This screw adjusts air.] Idle speed screw, faces outboard, at the top of the carb; set for 450 rpm, and make sure the governor correctly engages the slot. [This screw adjusts RPMís.] Final settings are determined as follows; Get the engine warmed up, and idling.
Turn OUT the idle air-mixture screw until rough running, then turn in until it idles smooth. (Mine is set at 1 turn open.) Rev it up, wide open, warmed up, then turn the main fuel adjusting screw IN until rough, then out til smooth, then 1/4 turn to 1/2 turn further out. (Mine is set at 1 turn open. Other advice has been to set it at 2 1/2 turns open for pulling implements.)
Should rev up smoothly and evenly. Too Lean = stumble, sputter, damaged melted plugs.
Correct = tan plugs.
Too Rich = back smoke, black sooty plugs.