Hello from Taiwan!
First time builder. Bought a 66cc kit from China about 2 weeks ago. $190 with free shipping to Taiwan. I then bought a cheap mountain bike online, but when I tried to install the motor I discovered the frame was too small and also the front part of the frame was not tubular, so I returned it. I then went online and looked for used bikes. Found one that looked kinda old, but the frame looked perfect. Called the guy up and said I'd like to buy it. No problem. As I was saying "see you later", I mentioned that I was going to put a motor on it. He surprised me by saying that that was exactly what he used the bike for! Huge coincidence since I've never seen a motorized bike here (been here 25 years). The bike was 25 dollars.
The only problem I had building the bike was with the rear sprocket. I could not get it true. It wobbled...and in my efforts to get the high sections lower I broke bolts. Bought some replacements, but still couldn't get it true. I later discovered that the rubber washer under the sprocket had quarter section that was at least half the thickness of the rest! I don't know why I didn't notice that. The inside rubber washer was the same thickness all around. So I swapped them. I also cut a piece of inner tube to place between the spokes and the inner washer where it was thinner. That worked well and I was able to get the sprocket true and aligned!
After only running the motor an hour or two, fuel started flooding out of the air cleaner. I knew this had to be something wrong with the float. So I took off the float case on the carb and saw the problem right away: the plastic float doughnut was full of gas! Bummer. I contacted the shipper and they said they would send a replacement carburetor, but I said I only needed the float. They said they would just send me the whole thing anyway. lol
In the meantime I read a post explaining how to temporarily fix the float. First heat up some water, not quite boiling, and submerge the float. The air inside expands and you can see where it is leaking. Mine was leaking from the inside seam. Mark it. Then drill two tiny holes on opposite sides of the float to drain the gas. Then melt a bit of a water bottle cap over the holes and where the leak is. This kinda worked, I don't think I perfectly sealed it but good enough to ride a bit before the replacement comes. I just ride for awhile and quickly turn off the gas and then drain the the float bowl. Yesterday I rode up to Yangmingshan National Park. About a ten mile cruise. So awesome!
Hope that isn't too long of an intro. Glad to be part of this community. Pic attached of my ride...