question about exhaust residue

[Skeeterbait]

2B225158 – 2016 Mercury 115ELPT Fourstroke - 14 hours

Running on 87 octane ethanol free, 1 oz quick clean and 1 oz quick care per 5 gallons.

Swapped out prop today. Looking up inside the exhaust port in the lower unit I was surprised that the exhaust residue was so extremely black, suety, and seemed a bit oily when rubbed between the fingers. Not a whole lot of it but was just surprised at its color and consistency from an engine not burning oil in the fuel. I expected a cleaner burn. Should I get the engine checked out early or is this normal?

[EuropeanAM]

How much of your 14 hours has been at 3500 RPM and above?

Excessive low-speed operation time will contribute to carbon/soot buildup (and can also prevent rings from properly seating).

While keeping the above in mind- we must also remember that the propeller bore is essentially the "tailpipe" of the exhaust system.

[Skeeterbait]

First 10 hours I tried to follow breakin procedure. I would think that 75 percent of the 10 hours was as 4000 to 5000 RPM varied with the prescribed one minute 6000 rpm runs. Last 4 hours have been a fair amount of idling around off plane. Probably 50 percent off plane and 50 percent 5000 RPM.

[EuropeanAM]

Last 4 hours have been a fair amount of idling around off plane. Probably 50 percent off plane and 50 percent 5000 RPM.

That's likely why you are seeing more exhaust residue.

[Thundra]

Running the Mercury Quikleen or Quikcare, Startron or whatever ethanol/carbon fighting liquid one chooses, helps greatly with the prevention of exhaust residue.

I get Startron when it goes on sale and stock up and use it with every gallon of gas I use and the barrels of my props stay clean. I also run at 3,500+ and WOT as much as I can, when I can.