What do you think might be causing a black residue in the exhaust of a rather new .90 sized 2-stroke. Broken in right, now running Omega Coolpower 15%, and a 13-6 prop. Engine starts fine, runs fine, idles fine, is reall OK, I just worry a little about her.

Overheard at the field (about a bipe): "It glides fine, it just doesn't move forward"

Guido:

"Black Stuff" is usually finely powdered aluminum. And it's not unusual on an engine that isn't completely broken in.

It could also be from the joint between the engine and the muffler. Pull the muffler, see if the mating faces show a polish. Remount the muffler with a thin film of RTV on the faces. Gaskets here usually fail in a short time, leading to loss of the muffler when the screws come loose and fall out.

Bill.

PS: Omega nd Coolpower are different fuels. Omega uses a castor oil blend, CP is all synthetic. They are both packaged by Morgan Fuels. I personally wont run CP without adding castor oil to it, three or four ounces per gallon. wr.

It can also mean an over-lean condition, I changed props (from 13 x7 to 14 x 6) on an Irvine .72 that has about 5 flights in it and sincve it is in a pipe it is hard to tune by sound (I forgot my tachometer [:'(]) so i put it in the air and although it was sagging a bit when it comes off the pipe it fle well.. after te flight I checked and to my dismay the residue wsa black and smell a little of burnt castor. I use Mach 7 (Omega) fuel 5% Nitro, with the 13 x7 the residue was dark blueish (mach 7 is blue in color) so I re-tuned thte engine from fully open and flew again. mucho more consistent, less bog down coming off the pipe and after a 2nd flight the residue was lighter in color.. still too dark for my liking but the burnt smell was gone... i will tune it a gain but will bring my tach along!
enough ranting

I would use Omega, better protection of the two. And even Omega burns dark. I switched to Byron fuels. They seem to burn alot cleaner. My 2 cents worth.

Thanks guys:
i miscued re fuel, as i have used both over the years. I believe the muffler/engine seat is at fault, as it has only a very thin gasket, and "black stuff" seems prevalent at that joint. I'll remount and seal as recommended. Also re prop: IMO I am turning a bit fast, definitely not overlean (kinda known at the field as mr. rich, and it ain't because of $$), going to fit a 14x6 now that I have a little more time on the engine. ( A 14x6 is not in the mfg's recommended range, so I toned it down a bit during breakin).

Once again, thanks to all- -keep 'em flying.....

The muffler on my barely run in Irvine 53 came loose and I think led to a lot of black deposit in the oil. On the other hand, I had some dark deposits in the oil after a flight this weekend and one of my clubmates told me that it was normal for the Irvine to burn oil. Motor runs fine despite the gunk.