Do you want to build a motorized bicycle? This should mean that you are a smart person because you have come to seek answers in the right place. It takes some prudence to not rely on the stock Chinese instructions that come with your motorized bike kit; they are quite bad and usually very wrong.
If you want a motorized bike that you can rely on and not just some delicate toy, there are a few things you can do to get a professional motorized bike.
These are not so much as instructions as they are more like commentaries on the parts of a 2-stroke motorized bike; how they should be installed, how they should and can be replaced, and just how they can be removed. If you have read the usual build instructions that follow the kits and the ones that can be found on the internet, this should prove to be a bit more helpful.
The stock tank that comes with the kits is usually quite good. They are usually referred to as either the “teardrop” tank or “peanut” tank. And when we say that they are pretty good, we mean that they are pretty good for what it is that they are, which is solid and professional. They only fail when the owner does not properly install them.
The weakest part of the fuel tank is the studs. They are mostly just spot welded to the tank itself, and although that usually is not an issue, it becomes a problem when you over-tighten them and use rubber padding underneath the tank (so that it does not get to slide around).
The use of rubber padding is not a good idea because it creates more pressure on the studs and, with the normal engine vibration, there are small cracks that will form around the weld joints on the studs that will cause the fuel tank to leak.
One best way to avoid problems is not to use rubber padding but you can put some double-sided tape or some adhesive on the bottom so that the tank does not slip around the frame.
Make sure not to over-tighten, but you should tighten it enough to keep the tank firmly on the frame of the bike. If you can, you should double-nut the nuts on the studs so that they do not come loose. You can also make use of a thread locker.
If you find cracks in your fuel tank, do not try to solder the cracks unless you have some professional soldering experience. A common complaint with the stock tanks is that they usually come with rust and metal debris inside them.