So my Puch has been running great for the last few hundred miles, so I decided to modify the stock 50cc head to work better with the 70cc airsal. I decided to put a large 4 degree chamfer around the outside of the head making it the same bore as the piston. You can see in the first pic why that lip is a big deal:
With the head chamfered and "bored out" to the correct diameter, the fuel air mix will flow much better and would act as a squishband. Before I attempted this, I made a CAD drawing of both the piston and head, so I knew before hand that I would be able to mill the head down over .025" before getting too close of a tolerance. In the end, I milled about .02" to raise the compression from the initial 125psi to 150psi.
With this "squishband" it took out any and all of the ticking/pre-detonation that was heard at mid to high rpm. All I can describe the sound as would be what the kstar kits have as "engine noise" or ticking. It also gave me a small but noticable mid power. It now sounds smooth, like putting in fresh bearings and removing piston slap. When the head was off, all of the ports were smooth, crosshatching was still noticable, and no scratches or any imperfections were seen. Over 1,000 miles on the kit and still going strong. Joe