Jim, the MC9's came with flatback carburetors, it is a diaphragm pumper carburetor, it sounds as though you should rebuild the carburetors with new diaphragms, set the fulcrum height and popoff pressure. If your engine has any type of air leak you will also have a problem with the fuel flow and keeping it running, not to mention if you run the engine in that condition, it is a candidate to stick a piston. If you have the equipment do a pressure check on both your engines. Terry Ives can supply you with the rebuild kits for the carburetors.