In addition to and restating some of the above: It could be that your gas tank has crud in the bottom and is clogging the pickup tube in the tank when the fuel pump sucks the gas to the engine. You could have the same situation just before the fuel pump, or up by the carb. It could be that your fuel pump is indeed going bad. If you have a fuel filter anywhere in the system it could be plugged up. Stuff could be inside of the carburetor. About the only way to diagnose what is wrong is picking points in the fuel system and inspecting them. I'd start at the carburetor or fuel filter(fuel filter first if you have one, not all did) and then work on back to the fuel pump and lines to the tank. Good luck, and someone with more experience may come along and tell you more specifically what could be wrong but I'm not sure exactly what's wrong so...
Good luck and I hope you find what's wrong with it.
