I have an RCSSV50 from TBM on a CMP 74in Extra330L. Has about 3/4 gal at 40:1 through it, but still blowing black oil. 22x8 prop. Starts great, responds to the throttle well. I'm using the ignition that came with it, but I chunked the no name plug that came with it and used a CM-6. 1400 4.8 vdc Nimh battery. My problem is that it doesn't want to lean out properly. It will miss and sputter but keep running. When I try to lean it out, it will go lean before it quits sputtering. I have checked all the tubing connections for leaks, cleaned the carb screen, and checked the plug cap for tracking. No help. HOWEVER, when I pull it vertical, it will smooth out and climb right on out of sight. Goes right back to sputtering when returned to level flight. We thought maybe the added prop load while vertical helped so I installed a 22x10, but it didn't help any. Anyone have any thoughts?