25 hp merc tiller black oil coming from inside prop area??

[mikemac10]

After I use the boat and it sits for a while the motor starts to leak a small amount of black oil from inside the prop/exhaust area. What would cause this? Is my gas mixed too rich or might it be something else. Also I'm getting a little surging at higher rpms, I put in a new fuel line and bulb, and also a new fuel filter, and have run fresh gas through it with seafoam. Any ideas are appreciated, thanks.

[JaguarJim]

Hey Mike, sounds like leakdown from the unburnt fuel/oil in the cylinder walls. I have a 25hp on a tracker I use for powerplant lakes, and it does the same thing. I think Merc recommends running them at 50:1 gas/oil mix, of course you can run it richer, but then you'd really be getting oil running out of the lower unit. As for the surging I'd check the carb as to how clean the jets are. This junk gas everybody sells these days, I've had to rebuild almost every small outboard I've owned because of dirty/junky gas. Also you might need a rebuild kit, it has the new gaskets/seals for everything as well as a new needle for the jets, most of the time its the Idle Circuit thats dirty or clogged. And, from what I remember the rebuild kits less than 30 bucks. If you're motor is older, some of the Merc/Mariners are actually Yamaha's built to Mercs specs. and you can cross reference that by looking at powerhead numbers from the year, and in some cases the powerhead will actually have Yamaha stamped on the block, or the carb body. Hope that helps. Jim.

[mikemac10]

OK thanks, the motor is a 2001 and I dont think the carb has ever been cleaned on it.

[njj502]

Mine did the same thing at break in. Ive since switched to penzoil premium plus oil @ 50:1 and i run the snot out of it. No more crap out the exhaust now.

[EuropeanAM]

OK thanks, the motor is a 2001 and I dont think the carb has ever been cleaned on it.

It's time.... and also wise to do the fuel pump while you're at it.

It's not uncommon (especially in 2-stroke models run for extended periods at LOW RPM) to see oily exhaust residue after the engine has been sitting.

Regular use of appopriate fuel additives, ensuring the engine is run at mid-to-high RPM's for a couple minutes at the end of each outing, and Mercury or Quicksilver Premium PLUS oil may aid in cleaner exhaust.