There are only slight ( and i do mean slight) differences between a "premix" 2 stroke carb and that of a four stroke If the carb is from a auto lub or a forced lubrication bike then there is no difference in the carb bodies PREMIX 2 stroke carb have a slightly steeper RAMP to the venturi and a lower main jet height... WHY. Well you need to have a higher velocity of air through the venturi to lower the air pressure enough in the system to allow the viscous premix fluid to be drawn ( atomiser style) into the air flow. as the low pressure air is drawn over the jet the viscous fuel is "dribbled" into the centre of the air flow as the air flow is LAMINA it is escential that the fuel is delivered into the main air flow. As straight fuel has a lower viscosity than premix you do not need as high a venturi velocity to gain a low enough air pressure to vapourise the fuel; Also this is assisted by the EMULSION tube into the float chamber( that funny tube with holes in and the main jet at one end) also due to the lack of viscosity the jet height does need to be nearer the centre of the air flow and so you tend to get a higher main jet height Also calling it the main jet is WRONG it is technically an ANVIL, the main jet is actually in the bottom of the emulsion tube in the float chamber The emulsion tube actually allows the fuel to "BOIL" in it due to the low air pressure caused by the venturi effect. So to answer your question YES a two stroke carb will work on a Four stroke engine, Just rejet and change the emulsion tube for one from a 4 stroke carb PS by the way if you are suffering fueling problems of an engine everyone goes for the main jet... WRONG check the cleanliness of the holes in the emulsion tube, Clean holes mean the fuel boils easier in the tube Dirty tube and it SUCKS ( syphons) way too much fuel from the float bowl through the main jet