I have had similar problems before check and make sure your slides are in facing the correct way, notch to the air filter side(chances are if it was running a couple minutes with out this isnt the issue.. but worth checking), but when I first mocked mine up, the thing would run rough as shit.. turned out that was the issue.. and also make sure the choke tube linking the carbs is intact I accidentally knocked mine off except my right cylinder wouldnt fire correctly....