Murdo, thanks for the tip on the rims. I'll check that out. I've got to see how many spokes the original rims have on them and see if any of the Asian options will work.
Mark...on some research, it appears a number of manufacturers used the Sachs 50S engine including KTM (Comet), Hercules (K50 and others), DKW and Batavus.
There were other Sachs engines made around the same time for other similar bikes including the 501, 502, 505, etc. Some of those had pedal start and were installed in mopeds (Sachs Seville, Balboa, Westlake, Sparta, General 5-Star, Eagle, Hercules and even some KTM mopeds). The most common Sachs moped motor in the US is probably the 505, I think.
Anyway, I believe that the 50S, however, was among the most powerful as Jan points out (6.25hp) and has kick start and a 5 speed trans with a multi-plate clutch.
The 50S had at least two generations (maybe three) with the early generations having cast iron cylinders and smaller cylinder heads. The last version of the 50S before it went to water cooling had the head with the huge radial fins as shown in the photo above. Most people think it's a 125 when they see it.
These Batavus / Starflite bikes were apparently sold at big stores or from catalogs in Europe back in the day to compete with Garelli, Puch, Honda and some others that had strong 50cc "light motorcycle" options. There's a really neat article from the mid-70's that pits them all against each other in terms of power, handling, etc. Fun stuff!
