I am having the same problem with my GB 330 I have an OS160 installed and it will lean and die at about 3 minutes into the flight. I have tried the same remedies, large bore tubes and a short run. I did find that the needle valve was vibrating to a different setting in flight so stabilizing that helped a bit. Richening the low end helped. The desighn of the plane puts the tank axis below the carb on a side mount set-up. this probably is a major part of the problem. A pump might do the trick here or use of a header tank.