This could be a lot of things. Water in the gas, bad fuel pump, fuel line blocked, fuel filter, carb problems or out of gas. First test is for fuel to the carb. Unhook the fuel line to the carb and stick it in a clean, dry clear bottle, like a pop bottle. Have someone crank the engine, you should get gas flowing. If it flows, and is clean, check the carb. If it's dirty, you need to drain the tank, clean the lines and the carb. If no fuel, does fuel flow from the tank, then to the pump.
