230 engine backfired, now wont run

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??????????

Did you set the timing properly? Mine had a similar problem.

It was orginially set right and the thing started right up, but we havnt checked recently, we are gonna look at that tomarrow

Sounds like its loadin up. My 02. Check the carb.Carbon is a big issue for some reason on theses motors,check the plugs for chat.