I must disagree with the timing running back to close to TDC Bultacos will kick back and run when set 3mm or more BTDC 2t engines run both ways Villiers fitted to Bond mini car did this as they only had forward gear so to reveres the engine was started backwards using the starter I have a BSA B33 with manual advance retard If the lever is not set right and is to far advanced and kicks back you can have at least a sore ankle or knee (hitting the bars ) or really bad a broken ankle after you come out of orbit Fortunately 4t do not run backwards