Unplug the line, hold it by your carb, turn the petcock on. Look to see if fuel comes out, go from there. Clean your tank really well, examine fuel delivery petcock , is the filter clogged ? And if none of that works change your engine seal off the crank. If your bike is old, and if the carb ever got dirty or clogged you have to blow it hard in the tiny holes with compressed air at an automotive place, or use a good air compressor or you'll never get it to work right. I've had to do that a few times.