Your reasoning is logical but this is not how the 2-speed Puch works. The first gear centrifugal clutch can only come into play when the crank shaft has reached an RPM which equates to several MPH. The second gear centrifugal clutch weights are actuated when the rear wheel reaches a speed of around 15 MPH (depending on the sprocket sizes you have) BUT, the second gear clutch requires that the first gear clutch be engaged in order for it (2nd gear clutch) to engage the wheel to the crank. It is kind of complex but actually a very clever way to deal with the problem of keeping the transmission from shifting back and forth between 1st and 2nd at a certain engine speed.
Some Puch engines have a decompression valve but most don't. It is not necessary, and can cause problems. I would suggest disconnecting the cable going to it. Mine starts fine without a decompressor and I have even raised the compression ratio quite significantly (11.1:1).