Yup – that gasket Mercuryman mentioned looks like a small, thick, compressed fiber washer, and it can fall on the floor when the carb gets disassembled or re-assembled, but my experience with missing "donut" carb gasket is OK at idle, floods and quits when throttle is advanced. With your symptoms, I’d say the gasket is there but not sealing completely. It sits at the bottom of the casting that extends down through the hole in the float. When you screw the float bowl to the carb, if you carefully squeeze the bowl to the carb first, you can feel this washer compress. It prevents gas from bypassing the high speed jet.
Dave