not the cold or old gas.
turn the petcok off and then pull the fuel line off the carby.
Don't lose those litttle clips. hold the line over a can and turn the petcock on and see if it runs freelly. Now try it on reserve.
If it runs freely to the carb, but it doesn't get to the cylinder it is time to clean the carb. If it doesn't run to the carb your problem is at the tank or petcock. give it a try and let us know.