By thesounds of it you have theratchet type starter that hgoes into the cowling. When you havethe cowling pulled off there is like a square thing that fits into the recoil mech attached to the crackshaft.
This unit that unscrews off the crankshaft may need disassembling and some thouough cleaning, it would not hurt to clean any sign of cossosion off the crank as well, then once it is put back together a verylight helping of light machien oil on the inside of the ratchet mechanism would help it from reoccuring.
