My 69 m715 recently got new rockerarms, timing chain,timing gear, camshaft, new head gasket... and a complete valve job.... Since then it has been running fine for a month.... now it wont start, the engine cranks but it wont stay going...we can see and smell the gas getting to the carb.... the engine started fine after this then died out and wouldnt stay running unless i kept moving the throttle. eventually it backfired really loud and we havnt been able to get it running since.... We pulled the valve cover off ...everything looks fine... took the carb off and inspected it...everything looks fine.. looked at the distributer everything is fine... the firing order is right, the cables are new..... Does anyone know what could be wrong... Im thinking the timing chain might have slipped but this seems unlikey???? I just dont understand what would cause it to stop running after a month?...............any ideas??????????