Gentlemen:
Would appreciate any of your observations on this issue from a learner. I have a relatively new OS 40 and have been getting it ready. I installed it in a plane now and am noticing that the exhaust spits black spots and blobs out and on to the wing and fuse. White areas are covered in gray. Is this a concern?

Fuel: Wildcat 10% Nitro with 80% Synthetic and 20% Castor of which I pour out 8 oz. and added 10 oz. of castor to make it compatable for my Foxes and Asian engines.

I have about 12 runs on it. I crank at 2 turns out and run it about 1 1/2 - 2 turns out. It starts quickly and runs very smoothly, and I get a very visible grey smoke from the exhaust. I'm very pleased with it, but is this exhaust sludge OK?

Thanks for your input.    Gene Elliott

Black normally is aluminum.

I would check to make sure the muffler isn't slightly loose and vibrating. That will make the small aluminum particles in the exhaust and make the mess.

It is possible it is still breaking in, but the OS LA's typically break in pretty fast.