It is normal for a crankcase induction 2 stroke to have resistance to rotation twice each revolution. One resistance is crankcase compression, the other is cylinder compression. If it doesn't have both, it won't run.
What you have described could be quite normal - compression always leaks away if you wait a bit - but it shouldn't happen noisily or quickly. As ken said, you may have a head gasket leak. If so you can probably locate it if you put your ear close to the cylinder head. It is also possible that you have a crankcase leak. If you have a crankcase leak there should be visible signs of leakage from the upper or lower crankshaft-to-crankcase seal. A substantial crankcase leak could cause your engine to lack power, be difficult to control with the governor, or even stop running.
It is normal to hear a slight pop when you turn the engine over, due the opening and closing of ports against pressure.
