Look for air leaks. Air leaks where the carb mounts on to the crankcase. Check the cover on the back of the crankcase. Check for any obstructions in the fuel system, like in the needle vavle assembly. Take the carb apart, soak it in alcohol, clean it up and reinstall it.

You did not say if it was a new engine or an old one stored for a long time.

Good luck.

Chip