I also have a 1976 Puch Maxi. My Clymer guide says:
1. Place moped on the center stand.
2. Start the engine and let it run.
3. When the engine is warmed up, turn the idle adjust screw with a screwdriver to reduce engine speed as much as possible so that the rear wheel does not turn (the engine speed should be between 800-1200 rpm). Speed up the engine a couple of times and let it slow down. Recheck to make sure the rear wheel doesn't turn.
4. The engine should not stall when coming to a complete stop on the road. If it does, readjust the engine idle screw to a SLIGHTLY higher engine speed.
I hope this will help you out.