1-Make sure you have the diaphram in the right orentation(make sure the nipple is down and the gasket is on the right side. check the meetering level. No trash in or around needle or seat.
2-Make sure you did not overtighten the carb bolts and crack the metal reed housing(check it very closely).
3-Make sure you have a good pulse line going from the carb to the engine.
4-Get a new plug and gap it properly.