ok this mean the mixture is already to rich and any added restriction to the airflow just makes it richer obviously,you need to check a few things,take the bottom of the carb/s off an have a look to make sure the main jet/s have not come loose and fell off,also above the main jet there is a small jet thats butted up against the end of the needle jet also somethimes its part of the end of the needle jet anyway this part wears as the needle rubs against it as the air is drawn through the carbs venturi in the inward direction and as it rubs it cause the hole in the end of the needle jet and makes it oval instead of round and this allows tooo much fuel to go up through it the only other cause is if the float height is set wrong this can cause overfuelling but it usually makes the fuel leak from the bottom of the carb.most likeley to be the worn needle jet end or loose main jet/pilot jet
adam bike doctor(of milton keynes motorcycle centre), November 2010
