Ok Im a middle age lady here who's learning the hard way. So correct me if I'm wrong. I believe its the fly wheel. I was reading the booklet and it mentioned sometimes the fly wheel gets a little stuck so try moving it with a little shove. My words not theres. Well i tried it and it ain't moving at all. Im not quite up to the chain part (still adjusting the engine on the bike) but thought maybe somebody can clue me in what to do?