I have a s stik with an os 46 fx, and the other day I notice for the first time that the blow-off from the burnt fuel on my plane was dark in color. It usually is still a little pink, since I burn Omega pink, 15%.......I did run about 85% throttle this time, I usually run around 50 to 60% throttle.........and I have only burnt 3/4 gallon on this new engine. Any ideas would help...

You just need to richen your high end a click or two. As long as the residue still feels oily, a slightly brownish tint is OK. If it gets really dark brown (burn't oil) or black (metal), you might have a problem. You should check your high speed needle at the start of the day to make sure its set correctly. Changes in temperature can make a big difference in your engines settings. Colder weather requires a richer setting, and vice versa.

Brad

To expand a little on bkdavy's comments, dark black exhaust often means there is metal-to-metal contact somewhere in or on the engine. I've had mufflers come slightly loose and was alerted to this because it caused the thick black goo to suddenly appear on the plane. I've also seen this when engines work themselves loose on metal engine mounts, but that's not as common in my experience. It's simple enough to double check your muffler (inside and out) and engine mounts if applicable. If that's not the problem, I'm sure someone else can give you more hints.

Omega fuel contains Castor oil. About 30% of the total oil content is castor and it tends to leave a darker residue than pure synthetic blends. Depending on how dark it is, all may be just fine.