Sounds like it is running to lean. The fact that you have tried 2 carbs & are still having problems seems to suggest that you have an air leak somewhere. Double check everything, all the joints, clean out & check the carb, set the H & L screws correctly. There must be something causing the lean mixture, so be thorough. Millions of small motors uses these carbs successfully so there is no reason why it shouldn't run well. Good luck