Sounds like you are either being starved for fuel, watch float bowl site glass at 2500 or so RPM and make sure the fuel stays in the float for at least 1 min. Or your accelarator pump is malfunctioning, look down carb when not running and watch for steady stream of gas when the pedal is engaged which should continue streaming after the pedal has stopped moving for a moment. Or last but not least you have a major vacuum issue, spray carb cleaner around your vacuum lines and the base of the carb and listen for changes in engine sound.