There is a small ball in the bottom of the accelerator pump. This closes when the pump is activated and forces gas under pressure into the carb throtle body. Look down the carb and press the accelerator to insure you have a good gas flow, if not this ball is missing and your not pumping enough gas to the manifold. This ball is overlooked a lot and was the cause of my problem, which sounded kinda like yours. Hope it works for you. Keep us informed..
