The first thing i would check is unplugging the fuel line and vacuum line at the carb and and sucking on the vacuum line. Put the fuel line in a bottle and you won't get anything in your mouth. Fuel should flow out of the fuel line pretty easily! If it doesn't the screen between the petcock and fuel tank may be clogged, or the fuel filter. If fuel does flow easily you may have a vacuum leak somewhere between the engine and the carb.
