I bought a Harbor freight for stroke, with the idea to simply mount it behind the seat of a bicycle that I have not bought yet. Similar to the minibikes I built many years ago. Just a centrifugal clutch and chain down to a sprocket on the rear wheel. But I notice that nobody does that and I haven't seen one motorized bicycle set up like that. It seems like a very simple, easy way and I'm wondering why it's not done? Can anyone tell me that?