Disconnect the linkage at the carburetors, and check the linkage from the foot pedal all the way to the carbs. It should smooth with no catches or scraps, if there is make some adjustments. Check the levers on the carbs are they free and easy? I have found the butterfly rod going through the throttle plate was too tight (my opinion). The sticking would get worse as the engine got hotter. I sprayed some lubricant in that area when it was sticking and it freed right up. I took the carbs off and set them on edge and put lubricant (marvel mystery oil) on the shafts so it would run down inside. That freed them up, and every once in a while when the engine is hot and it feels a little sticky I give them another shot. Also, you may need to put a stronger return spring on your linkage. If your running the original spring those springs get weaker over time.
