I would think that since you cannot lower the tank, you probably need to invest in a, "Cline" fuel regulator. Your situation is similar to running with an, "Over primed" engine. In other words, the engine is, "Drowning" in fuel constantly due to the siphon effect. The fuel regulator will alleviate this problem. It also occurs with 4 stroke engines as well. I had to use an on-board glow system on my H-9 P-47 for the same reasons. I am running an OS 91 Surpass II and at anything less that 25% throttle, mine started to smother out. With my 4 stroke, the on-board glow system has pretty much cured the problem. I am looking at either making or buying a tank that will fit into the front bay of the fuselage and have the tank centerline at the same height as the carb. This should enable me to not run the on-board glow.