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I just recently mixed my own glow fuel for a 2 stroke O.S 46AX. 20% Castor + 80% Methanol by volume. I just finished tweaking my low and high speed needles to get a good performance out of that fuel. I have however a doubt about the color of the oil that comes out of the exhaust. I'm attaching an picture of the kitchen paper I used to clean the slime off the side of the plane. Its a pale brown/grey. It seems odd as the fuel I purchase at the local hobby shop produces only pinkish oil as the fuel is red colored. There are no dark traces in premixed fuel. I figure this may be due to the synthetic oil content of the premixed fuel. When I look at the cloth against light its translucent, but is definitely darker than the regular premixed fuel's oil. Is this OK or is it a sign of some mistake at the time of mixing?

By the way, I got more rpm's measured with a tachometer that what I used to get with 5% nitro [8D]

aerowoof

brown is normal for castor oil,black usually means metal to metal contact somewhere usually a loose muffler.you will find that the engine may be stiff if not used often this is just congealed castor oil and a little new fuel in the carb will free it up.beware of using cstor in abc engines as the varnish build up can cause problems.

bigtim

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if I recall it's a new engine you will find the black oil will become less as the engine becomes more broken in at least mine did for my OS 46 AX as long as there is oil coming out the pipe your good.
I think I mentioned this in another post but I will again, I also noticed less black oil when I switched to a cooler#8 plug also

downunder

Not true, what you'll find is a layer of the brown varnish (which is a lubricant) on the piston skirt but the small area near the crown where the piston actually seals (usually about 1/16" wide) will be a normal piston colour. Some synthetic in the mix is supposed to stop the varnish layer but I've never used a synthetic so I can't comment on how well this works.

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The engine has now about 250 solid minutes of flight on purchased mixed fuel with 5% nitro. This issue arises now with homebrew fuel.

B.L.E.

Commercially mixed all castor fuel also leaves brown exhaust deposits. This is the result of the heat caramelizing the castor oil. Synthetic oil doesn't caramelize, it simply vaporizes instead.
Occasional disassembly to remove accumulated varnish is a fact of life with castor lube.