the bing will run rough if the mid range jet gets plugged on the vent. The vent goes to the inlet of the carb right where the filter hooks on, it has an opening of lets say .020. it is really small. The best thing to do is remove the bowl and take some carb cleaner and remove the jets and spray into the hole, you will see the stuff coming out the vent. your done and you will be supprised at the difference in the runing of the engine at mid throttle. I usually do this at oil change and I also take all the other jets out and spray the circuits. hope this helps.