Air intake noise made my jaw drop
I happened to have my head down at engine level while revving up motor, and couldn't belive that nearly all the noise came from the intake. ("80cc" powerking stock setup). Since the speed of sound far outpaces the speed of ehaust gas flow, when the piston is down and intake and exaust ports are both open, the noise travels right out the intake. (I'd been wondering why it seemed like oil was being forced out the air filter!)
I did some Googling about mufflers, and found I was mistaken in thinking they utilized expansion of gas to quiet things down. Now I know that they use pipe dimensions to cancel out sound waves that bounce around inside..
So, the next thing I'm gonna try is to make an intake muffler, soldering a 3/4 inch tube, crimped in the middle and drilled on either side, soldered inside an aeresol can...basically making a muffler for the intake. Of course, the volume of flow will not be reduced, keeping in mind the stock intake manifold diameter.
To make install easier, I'm thinking of using car radiator hose to match the nearly two inch carb existing inlet, which would also match aeresol can diameter.