Take the fuel line off the carby and put it in a plastic container. Now crank the engine. Is any fuel coming out? If there is youve eliminated everything previous to the carby.

In the carb could be a sticy float valve. The carby probably has 30yrs of crud in it anyway so geta workshop manual and strip the carb, clean everything with carby cleaner and reassemble. Could be a blocked jet or something. As said above could be the carb filter too. Or the anti dieseling solinoid as they are pretty common to fail! I think only the really early 1000/1200 carbs didnt have the solinoid.