Black "stuff" from 4 stroke exhuast?

[heligrom]

just noticed this today when flying my Thunder tiger 91 4 stroke.

there was this black, oily substance on my firewall and wing after my third flight of the day. i noticed that after that flight, the exhaust coupler was loose where it attached to the engine. i tightened it down and went to fly again.

engine ran great, awesome power plenty of smoke, not overheating at all just doing exactly what a 4 stroke should.

however, once i landed again i noticed this black oily substance in the same spots as the previous flight. this time the exhaust coupler wasnt loose so i was surprised to see this stuff. however, i did notice that on the rocker covers there were two cracks where it looked like the valves hit the inside of the cover whilst running. i thought that maybe some oil had leaked through but upon removing the cover, it showed no visible hole

so does anyone have any ideas what this black stuff could be? most guys at my field say its just exhaust leaking and that i should seal the coupler with RTV silicon.

the engine only has about 1.5 gallons of 15% omega through it. HSN is about 2 and 3/4 turns to 3 turns out. im not sure about the LSN. runs smooth, spinning a 15X4 W APC prop at around 9900 RPM. transitions are smooth and she comes down not hot at all

any info would be great. thanks for the help!!

[Unbalanced]

Castor goo...

[TheTank]

Typically, if the oil is black, there are metal parts in it. This often happens when you get a loose exhaust or such, or can be signs for a larger problem. If its coming out or around of the valve covers, I would pop them off and take a look. They just may be loose. It something in the valve train had struck the valve cover, in most cases, you would have known it long before you got it on the ground. Also, richen your mixture up a bit. It really takes a lot to make castor oil turn black, so I doubt thats the case, but its worth a shot. You could be detonating and running really hot.

[Vic3D]

Like Tank said. If everything else checks out then you are running too lean.

[heligrom]

thanks for the info guys!

i actually just ran the motor before, and after referring to the manual (who uses those things??) found out i was running the motor wayyyyyy too rich. they suggested 2-2 1/2 turns out and i was at 3 1/2 turns out. leaned it out to 2 1/2 and she ran awesome! great transition, more power then before plenty of smoke and didnt get hot

i think running it too rich may have caused the problem which i found to be surprising. i'm also going to re adjust the rocker clearances as i found that they did supply me with the gapping thingys