I would say check the needle valve orings.thats the last place everone looks.check around the carb venturi.make sure that gaket is good.But first check the glow pug gasket. Also one more thing.Take a spray bottle with water,get the engine to idle the best you can(engines dont like to idle with an air leak.)and spray around head carb(but not in the vent.) back plate etc.The engine will stall almost imediate.That should show you your leak.