Try turning the idle mixture screws in slowly and GENTLY on the center carb while it is idling until they bottom out GENTLY. If it stays running with both of those screws in all the way you will need to work on the idle screws on the outboard carbs also, they may be hidden and coverd up in the base plate with lead plugs The carb. list numbers are on the back side of the carb main bodys on the passenger side right below the air cleaner base rings Another thing to check is with the motor idling and the air cleaner off is to look down all three carb tops and see if you see any fuel dripping from the boosters that hang into the center of the carb. If so that should be your first thing to correct Let us know what you find