OK, you know that idle timing is too far retarded. If advanced timing is also too far retarded, your cam chain is worn (as the cam chain wears, the tensioner pulls the camshaft and with it the ignition rod clockwise. If wear is bad enough, points can't be advanced far enough to compensate). If advanced timing is correct, excessive retard at idle is caused by wear at the tips of the bob weights. Plenty has been posted on this, seek and find.
Edit: Right, as Gary notes, correct advance timing is important because if advanced timing goes past 40* you'll be at risk of holing a piston. However with idle timing too far retarded, you'll experience hard starting and carbs popping out of the boots. Also right, playing with the gap will buy you a little slack, but it sounds as though your idle timing is almost at the TDC mark.