Well, I have encountered the problem often enough that I just provide a remote static air pressure source for the carb as a matter of course in my building. I have even seen problems with uncowled airplanes that have the carb diaphram cover facing the prop blast. In the small engine repair manuals, it is often stated to be sure upon reassembly that you don't have the carb reference pressure hole in the cover facing the cooling air blast from the engine...

Some Walbro carbs come with a fitting for a hose on the cover from the factory. I'll try to get a chance to look through my carbs tomorrow and see if I can come up with a Walbro part number for a cover with a fitting. I just solder a brass tube into mine usually.

AV8TOR