Millertyme2000, here is an update on my situation that may help you. We have worked on my new OS46AX on three different sessions. We started with checking for air leaks at the tank, replacing glow plugs, changing to different size props, numerous high and low idle adjustments and this is what we found the culprit was tonight. First, my new Sullivan tank cap screw was a little loose, the screw was stripped on the inside backing piece. Installed a bigger screw and it snugged right up. Second, the high speed needle valve was machined wrong from the factory and the where the o-ring seats it's too wide and the o-ring can easily be moved back and forth. Typically, I've seen snug fits on the o-rings and when they move or rotate easily it's time to replace them. I swapped out my hsn from an older OS46FX and we went over all the adjustments (low and high) and it ran fine. So, I need to order a new hsn valve or find a second o-ring that will fit behind the first. I was ready to take this engine off and ship it back to OS, but after two successful flights to near empty I think we finally found all of the air leaks. You might want to check yours, hope it helps. DG