Re: what did you do to your motorized bicycle today?
Another issue with the rear axles on these are that they're live axles which makes turning an issue but that problem can be fixed by making up a differential so each axle half can get power from the engine but they can spin independantly from eachother... I saw one build where the builder made up a differential by splitting the axle then using a freewheel on each axle half so both wheels can still get power to them but during a turn the outside wheel will be able to spin faster than the inside wheel. His setup wasn't a true differential per se but it did the job just fine, in the middle of a turn, power only goes to the inside wheel since the outside wheel is allowed to spin faster.
This can be done using a set of freewheels on each axle half and running 2 sprockets from the intermediate shaft and a chain to each freewheel, or a more conventional differential could be used like those found in some older 80's go karts and atv's