interchangeable

I recently swapped out a motor on my friends motorized bike because his motor needs a top end (cylinder, piston and rings). I want to rebuild the engine but my friend does not know whether it is a 49 cc or 68 cc. Is thier any way to tell by measureing the bore or whatever? Or are the cylinder...

Is it possible to use a motorcycle fuel tank for a bike? It seems 1.4-2.5 liters is the norm for a tank, is there anything special on a 2.4L bicycle fuel tank that isn't on a 2 gallon motorcycle gas tank? Is there any kind of modification I could do to the gas tank to work with a bike engine?