smokey motor question

[DarthBaiter]

I bought a used 1977 johnson 15 hp. I took it out and ran it around and it seemed to smoke a lot and run rough. I loaded it back on the trailer took the cover off and noticed a spark plug wire was off. I put it back on, dumped back in water and it seemed to be a bit better but still smoked. I then took it out on opener and trolled around. It quit on me and i noticed the tank didn't have a vent valve so I opened the cap a little and I was able to start it again. Later in the day i noticed a black oily substance running down the side of the motor. I had enough of the smoke so I loaded up and then saw a black water line across the entire back of my boat. Like the oil was leaking out and where it met the water, attached to my boat. I then noticed a dark brown oil coming out the back of the prop too. What is going on? Did running it without the plug wire for 20 minutes at first and then not venting the gas tank lead to anything? The dealer where I bought it from a couple weeks ago said the rich/lean knob was set to go and i wouldn't need to touch it. Any suggestions on what I should try or what's going on?

Thanks in advance for any help.

[DarthBaiter]

Where is the edit button??? I forgot to mention I did mix oil 50:1 with fresh non oxy gas.

[Deershooter]

I would try to replace the spark plug in the cylinder that was unplugged. It could have fawled out with all of the fuel that went in there without burning. Then when you hooked it back up it would not burn all the fuel out of the cylinder causeing the fuel to leak out of the motor where it shouldn't. Cheap and easy to try first.

[boatfixer]

I would agree that that cylinder is loaeded up pretty bad. I waould replace the plugs to. All that excess gas/oil mix is running down the exhaust housing.

[Black_Bay]

My dad has a 15hp Evinrude that does something similar. I found a site that deals with smaller OMC's. One thing it says is: On the motor shown in the photo below, the owner had lack of power problems even after all apparent avenues were covered. Compression was 120# on both cylinders, carburetor was cleaned more than once. Fuel was mixed 50-1, but there was an excessive amount of black oil coming from the relief holes. What was found that the fuel pump had a leak in the diaphragm & was also pumping an excessive amount of fuel directly into the crankcase, which settled into the bottom cylinder and was subsequently going out that cylinders exhaust port & then into the exhaust housing of the motor." Search for sschapterpsa and then ramblings/johnson.

[Black_Bay]

Additional info: "Black or Gray Oil Coming Out of Upper Exhaust Vent &/or Lower Unit Holes : Many of these motors are basically used as a secondary motor, & usually then as a trolling motor, and are ran for considerable length of time at a lower RPM. The fuel oil mixture ratio of 50-1 is probably too rich by some. The black oil that seeps out of the motor is just unburned oil from the gas mixture. The black color is coming from the carbon created during the pistons firing situation & is accumulated unburned inside the exhaust housing. The excess oil in the fuel is mixing & softening up the carbon, creating the black oozing oil. You can reduce the amount somewhat by properly adjusting the carburetor idle jet to it's leanest position & where the motor runs best at an idle.

Or, it could be a 6 gallon tank that the fuel line is still attached to the motor & the outside ambient temperature is high enough to expand the fuel inside the tank to where the gas is forced into the carburetor & IF the needle valve is leaking, it will force fuel into the engine & out the exhaust which mixes with the exhaust carbon & leaches out as BLACK oil out the prop's exhaust.

This oil seepage may not be evident until a day or week after usage, & then will seep out up to a couple of weeks later. It seems best for most boaters to then simply live with the idea that you may have to wipe it down after each usage.

It is observed that if these motors are used on a smaller boat as the only propulsion, and act as a "get there" motor & also as a trolling motor, this black residue is considerably less to almost non-existent.

If you are getting a thick creamy gray oil oozing out the prop hub, it is essentially the same as above except the inside of the housing may have less carbon build up & therefore the color will be lighter. It is the same thing as described above, but possibly from a motor that may not have been run much for some time & there is not a lot of carbon inside the exhaust housing. The carbon is what makes it black. If there is minimal carbon built up from previous runnings, the oil will be the thick creamy light gray color.

Also if the engine was winterized with fogging oil then you would expect to see oil coming out of the exhaust because this would soften any carbony buildup in the exhaust system. If it smells like gas = unburnt 2 stroke oil. However if it smells of rotten eggs = Lower unit oil.

This many times may be confused with the lower unit oil leaking because of the color & location of the oil coming out. Another reason as to this also happening is as explained above under the Converging Ring on the prop, is if this ring is missing it can hurt by not creating enough suction to pull the oily residue out of the exhaust housing."

[DarthBaiter]

Interesting. Thanks for the info. The more info the better.