Sounds like our on the right track, but in some cases engine surging is not a sign of a rich running engine. Suggest checking your engine temperature, check the color of your spark plug, and make sure your baffling your engine correctly . Your exit air flow from your engine cowl should be at least a third larger than the intake. With a round cowling you should baffle the front of the cowling leaving only a opening in front of the engine cylinders .

Venting the carburetor maybe a treatment to the symptom of improper engine ventilation and not a cure to the true problem.