Black sooty smoke deposits?

[The Dunc]

I test-drove the 1988 Evinrude 90hp I purchased and found mostly good news ? but some problems. There is considerable black sooty deposit on both the underwater exhaust ports and the above-water. Checked spark plugs they look great and are the right numbers. Starts good, Idles well, high speed good, good power, but a little rough in midrange. Any suggestions on where to start my search for the black sooty stuff?

 

[freddyray21]

Re: Black sooty smoke deposits?

the black sooty deposits are carbon from exhaust. You can do a decarb on the motor and clean the ports with carb cleaner.

 

[The Dunc]

Re: Black sooty smoke deposits?

Thank you, Freddyray - I read another posting that noted this can happen when an engine has sat and then only been run a short time. I'll check into the decarb process.

 

[ezeke]

Re: Black sooty smoke deposits?

The de-carbon treatment needs to be done at least once a year, and should be followed by testing of the recirculation check valves.

http://forums.iboats.com/showthread.php?t=158076

You can help by using BRP Carbon Guard or similar fuel treatment specifically designed to keep the carbon deposits out of the firing chambers, and by using high quality synthetic or synthetic blend oil. Good, functional thermostats also help.

BRP XD-50 synthetic blend oil has a carbon treatment maintenance product built into it.

 

[emdsapmgr]

Re: Black sooty smoke deposits?

Check the idle operating temp on the engine. If it is running cold, it will not have optimal combustion and will smoke more. It should idle around 145-155 degrees. It could run cold if the thermostats are stuck open or if they were removed.