If the idle screw is opening the carb, AND he has had the engine apart, it sounds very possible that the piston is in backwards. When you look at the bottom of the piston, the "Skirt" only goes 3/4 of the way around. The part of the piston that doesn't go all the way down should face the back of the engine (Towards the backplate).

Someone else here (Names have been withheld to protect the innocent) had the EXACT same problem.