change

How do I change my fuel tank without fuel spilling everywhere when I take off the fuel line/ petcock, even if I turn of the flow of fuel on the petcock, there will still be fuel in the line running into the carb, how do I go about doing this?

If i have the entire kit that came with my 2 stroke engine, and wanted to get a 4 stroke, could i just get the engine and use all the parts i still have, sprocket, throttle, clutch, everything, on the new engine. and if so, would i go any slower or faster with the sprocket that came with the 2...