There are two diaphragms, one opens the inlet needle and the other, on the back side, is the pump..As long as the engine is running there is always fuel in the chamber under the inlet needle diaphragm..Excess pressure, more than atmospheric, makes it act funny..Most engines don't have the hole facing forward so the problem isn't there...Putting a shield over the hole in the cover is a good idea, another way to do it is to solder a tube in the hole and run a line into the firewall to dead air in the fuselage, as many do with 3W engines..ALL the ideas are good and worth a try...
The big carbs on the G26 act a little funny, when too rich they make the engine die fast, just like being lean...Sometimes going back to the beginning and re tuning both needles will fix the problem..I first saw this with the first G26, and the others I sold worked the same...