sounds like your pilot jet could be partially blocked, take it out and give it a good poke through with something then blow it through with air line or carb cleaner. whilst carb apart check needle height is correct , and float level adjusted correctly. You can find this info on dellorto website or eurocarb( i think) via google. when all is done and you have it running again make sure you have your air/ fuel mixture screw set right when idling, best to let the engine warm up a bit then turn the mixture screw in or out until engine runs a little faster, probably start by coming out first as this gives more fuel just a quarter of a turn at a time. hope this helps.