i dont think that's what you'd normally call a clutch.. it's a "starting lever". Once the engine starts, it has no useful function and engaging it while the engine is running is likely not a good thing to be doing..
Whatever you feel while slowing by engine compression might be normal or it might not.. certainly the bike, in gear, is capable of moving faster than the engine's top rpm under power.. But it depends on what speed you are talking about. A bike's top speed on level ground is close to the (safe) top speed down hills. Beyond that speed, even with wide open throttle, limits on the engines capability to pump air in and out comes into it. So, the wheels will turn the engine.
One thing to remember is that if you are flying down a hill and you close the throttle, no fuel and no lubricating oil is getting into the engine.. No oil down a steep hill while the engine is forced to be turning near it's top RPM is a bad thing. So, instead of slowing the bike just by engine compression, use the brakes too.
Grab the Puch manuals here