All my LA's do the same thing.Every 1/4 tank, I had to readjust the needle valve. I was running 10% nitro 16% oil. I went to 15% and it's not quite as bad. Once the fuel level gets below the carb, it has trouble maintaining enough pressure to push the fuel up to and through the needle valve. I have 2 .25 la's, 2 .40 LA's and a .46 LA, and every one of them do the exact same thing. Someone had suggested putting a check valve between the exhaust and the tank, but without a regulator and a pop off valve, I don't see how that would work. I even installed a larger pressure nipple, and the results didn't change. The only other thing I know to try is restricting the exhaust, but then you start hampering engine performance. All but 1 of my LA's is sitting on a shelf (next to my Super Tigre G75), and I have gone mostly to 4 strokes. I mostly put my 2 cycle OS' on a couple pieces of balsa or plastic that I'm glueing together so the wind doesn't blow it away.