G'day you have already looked at the number one thing it could be and thats the flywheel key...next is coil I guees .. Its very odd the saw doing this are you sure whoever is starting the saw is giving it a full hard pull on the rope,pulling it over slow and not giving %100 will make many a saw kick back like a mule and almost pull your fingers off very painful...They are 72cc and a very good old saw, Stihl still make them but now called ms381..Cheers