Here's the configuration: Zen 50 with a JettFire 50 & tuned pipe. Engine is mounted inverted. On the test stand this engine runs fine high & low. It will turn a 10X6 at 17.4K RPM. High needle set at 2.5 to 3 turns out. Low needle at the factory setting. Good transition. Installed in the plane the high needle must be set at least 10 turns or more to keep it from running lean. Can never get it go rich, 4 cycle, then turn the high needle in until it 2 cycles like I have done with my other engines for years. Idle at this setting is good but transition is not. It will usual die like it is starving for fuel when the throttle is opened. Adjusting the low needle doesn't help. Decided to try a new Perry pump that works off crankcase pressure. Followed the mounting & tuning instruction. Now the low end is very rich but the high end is the same, still 10 turns out even with the pump turned all the way in for max pressure. Back the adjustment out on the pump to try to get the low end straighten out but still very rich & bad transition. I have doubled checked all the fuel lines, no kinks or leaks. Removed the cowl so I can see everything, all looks good. Can't seem to find a happy medium. Any advise is welcomed.[&o]