Hello Guys,
I have a Evolution Trainer System engine on my first plane. It has been running great until a couple of weeks ago. All of a sudden the exhaust residue turned black. It was a pinkish color, same as the wildcat fuel I use. The fuel is 15% nitro, 80% synthetic 20% castor on the lube end. I also noticed a black residue on my muffler that wasn't there before. I had the guys at my club check my needle settings, and they are convinced they are set right. I agree from all that I have read about tuning an engine. I tightened up the screw that holds the muffler together, although it wasn't loose anyway. The engine runs great at idle or WOT, and transitions good too. I'm just worried about the black exhaust residue. Also, it has started quitting when it has about 1/3 tank of fuel left. This has caused me several deadstick landings, not something I'm crazy about. Any help would be greatly appreciated! You all have made this a great hobby to be in.

Thanks,
Dan