Here is a picture that shows how I made the tank.
I don't have a good pic right now of the top tube, but I made it out of two BMX forks, so the bottom of the tank sits down in it hiding the seam and the stopcock.
I like the 32 tooth for smooth vibration free speed. It cruises around 35 mph without winding out the engine. It requires some pedaling to start and on hills. I have not tried a 36T but I think it would be a good choise as well. It would require a bit less pedaling on hills, and since my motor does not have enough power to rap out, the 36 would probably go just as fast. I went with this 32 because I got it for free off of a childs bike I found in someones trash.

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