If it is a 2 stroke Happy Time or China Girl engine, you might have an air leak some place. Since it is new, it is probably leaking around the intake area. Use some carburetor cleaner to check for leaks, but be careful as it is flammable. You'll want to see if your idle speed changes. A fast idle may cause a severe lean condition and possibly cause over heating and a seized piston. Another possibility, you don't have the throttle cable connected right in the carburetor.
Good Luck,
Chris
AKA: BigBlue