Why would you want to restrict air going into the input side of the carburetor? That is the same thing as having the choke part way on. If it needs restriction in order to run rich enough, then it simply needs a leaner (smaller) jet and NO restriction.
A very common reason that small 2-stroke engines get low power is that their exhaust system gets plugged with carbon. This happens slowly over time and therefore is often overlooked by the rider. If your Puch has the stock exhaust system, clean it.
Remove the entire exhaust pipe from the moped. Take off the nut in the rear end and remove the inner muffler/baffle and clean out all its holes (not just the short 4 inch pipe in the end, but also the entire footlong aluminum canister inside). If it is stuck in the chrome exhaust badly enough you may have to drive it out. To do this wiggle loose the head pipe and pull it (and its associated rod) out of the main part of the exhaust. Now you can put a 5/8 inch diameter or so wooden stick (dowel rod) into the front end of the muffler and with a hammer, tap on the stick to drive the aluminum muffler/baffle out the rear end. Clean out all the visible holes then reassemble. Also be sure to scrape off any carbon that may be in the actual exhaust port of the cylinder while you have the exhaust off of the bike.
This has to be done from time to time, depending on the oil you use, the ratio you mix it at, and how you ride. A good synthentic 2-stroke oil will basically alleviate the carbon buildup problem. Well worth the extra bucks for this reason alone in my opinion.