re: 60 MPH...achieveable? Who cares?!? Let blueprint an engine!
I had an experience with crankshaft seals on a two stroke in the early '60s. It was on a Yamaha 175 motorcycle. Apparently it had originally been purchased in Japan by a US serviceman because parts weren't available in the US and its speedo was in kph. By the time I got it many miles had been rung up on it. It would only start if we towed it with a car or another bike. Once it started it would run at high rpms but if you slowed it down it would quit. After eliminating any problems with ignition and carburetion it appeared that bad seals were allowing crank case pressure to be so low at low rpms that there was very little suction through the carbs. When you tow started the engine it seems that the pressure changes in the crankcase happened so fast that there wasn't enough time for the pressure to fall that low and the engine would run fairly well. Unfortunately at the time I lived in an Eskimo village in NW Alaska and in those pre-internet days finding parts was impossible.
Goldwing 1500, Silverwing 600, Schwinn 49