Sorry for the late reply. I have only one shim. I believe it came with the engine. I have refrained from using higher fuel because I don't want to wear my engine out. One thing I have learned. I let the engine warm for about 5 minutes when starting cold. Dave is probably more qualified to answer this, but I would look at a few different things. before I start, I would like to note that I have the stock fuel tank and hoses from Hanger 9. The easiest thing to start with is this tank. Make sure that the fuel is flowing correctly, and the one way valve and fuel filter are working properly. If all is well, I would richen the pump. Perhaps the pump is leaned to a point that it is unable to keep up in the air. Since setting mine up, I have run in temps from 40F to 85F without touching any adjustments. I run Cool Power Synth 15%. If all of the above is fine, check out the pump gaskets to make sure the holes aren't obstructed, and the parts of the pump are in good working order.

Bob

Edited to remove non YS rep. response.