Is there an electrcal connection to the bottom of the carb float bowl? If so, check that it has battery voltage when the ignition switch is turned ON. If not, there's the problem.
If so, then I suspect the fuel shut off solenoid has either failed, or is gummed up and unable to move.
Unscrew it and bench test it.
If still no joy (or if there is no solenoid), you wll need to strip and clean the carb.
phil_saunders@bigfoot.com
Phil Saunders
October 2008