Honda outboard 15 hp crank case has 100ml of gas added after 3 hours of trolling

[Goodlumen]

800 mil of new oil will fill the crankcase to the half way mark on dip stick. After using the motor for 3-4 hours of trolling the dip stick will be at the full mark which means there has been 100mil of gas added. The dip stick will show darker oil colour and the back of the motor has black soot all over water outlet as well as my transom and main motor. Motor runs and starts fine other wise. Thought the problem was the fuel pump so I replaced the mechanical fuel pump with a electric low pressure fuel pump 3-5 psi. Same symptoms no improvement. Tried a spare carburetor with out any improvement. Removed carburetor held it in my hand and pumped bulb hard looking for leaks. Only time the carb assembly leaks is if I shake the carburetor.. I have ordered another needle valve for the float however I strongly doubt this is the problem. The needle valve looks fine and never leaked when I pumped the bulb. Also checked compression and have 125lbs of pressure in each cylinder. I am at a total loss — If any one has another idea please help — Paul. P.S. should also mention that the motor appears to be running rich because the plugs also have black soot. Trying a different carburator with different air fuel mixture setting showed no improvement . Manual says to set the high speed jet to 1 5/8 turns

 

[ahicks]

Have a look at the fuel pump....

 

[Goodlumen]

Removed the mechanical fuel pump and ordered a diaphragm kit to rebuild it . Made a aluminium cover with a gasket to bolt over the hole left by the mechanical fuel pump. Then I installed a low pressure electrical fuel pump to used while I wait for parts. I am still experiencing the same proplem. Crank case fills with 100ml of gas after 3 hours of trolling. I use this motor as a kicker

 

[ahicks]

Has to be the carb then....

 

[Goodlumen]

I have ordered the needle valve controlled by the float , I hope this fixes the problem. I have a spare carburator that I tried and got the same symptom. Both needle valves in my original and spare carb look good ? Strange thing is the motor starts and runs perfectly. Will troll slow enough to fish for walleye at 1.5 mph.. However I do get black carbon around the cooling water exhaust port 6 inches down from the base of the motor on the back? If the float valve fixes the problem I will post and let everyone know. Might be couple weeks , mail is slow here in Ontario. I have been waiting for 3 weeks for diaphragm kit to rebuild my fuel pump.

 

[ahicks]

The carb and the fuel pump are the only places that come to mind where fuel might be able to get into the crankcase. That's not to say there may not be something else. Might be worth a good look?

 

[Goodlumen]

My needle valve arrived , after installing and adjusting the float height I tried the motor. Same problem no improvement. I notice the motor was tipped forward on the transom so I made wedges so the motor is now slightly tipped backward , this too had no effect or improvement. Looking at a blow up diagram of my carburetor I had a one of those hmmmmm moments. The diagram showed a gasket at the back of the carburetor on both sides of a plastic coupling piece. I had installed this gasket in the front of the carburetor between the air intake plastic cone. This was the problem, This gasket was blocking out some air intake on the front of the carb causing the carb to run very rich. Human error was the cause of all my problems. I had installed gasket on the wrong side of the carb. Thanks for your help Ahicks — your comment that the carb and fuel pump are the only places that fuel can enter caused me to dig deeper into carb problem. Motor now running perfectly
Paul