How much is "almost"? Bottom line is that the engine is getting air from someplace. The knock-off engines are notorious for air leaks, and a likely spot for this to occur is at the base of the carburetor where it mounts to the crankcase.

Loosen the cinch-bolt securing the carb, and with your thumb over the air intake...press down FIRMLY on the carb body to fully seat the carb on the crankcase, and compress the O-ring. The O-ring is installed right?

While holding the carb securely pressed down, re-tighten the cinch bolt, and then give it another whirl.