I like the idea of the silencer/baffler bike. Also keep in mind that at least 25% of the noise from the engine is caused by the intake. If you can create a heavy plastic intake resonator box and use a foam filter (like on lawn mowers), you can quiet your machine a lot.
I plan to u-bolt a steel plate to a frame tube, with rubber spacers, the carburetor mounted to it (use a rubber washer for seal), and use ink pen tubes and machine screws to form a 2" gap to another plate, and jam a foam filter in there. This should make filter cleaning easy, and cut some noise.
