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Decarbonizing an outboard?

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#1 Gary B

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Posted December 14 2004 - 5:14 PM

Hi Guy,
What is decarbonizing an outboard motor and how is it done?
Thanks for the info

Tight Lines

Gary B

#2 Bottomline

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Posted December 15 2004 - 10:30 AM

Decarbing is a 2 part process. The first part is preventative, done by using a fuel additive to prevent carbon build up. SeaFoam is one such fuel additive and can be found at most auto parts stores. It also works as a fuel system cleaner and can be used as a preventative maintenance procedure.
If your intent is to REMOVE the existing carbon buildup from the cylinders, heads, and rings, a spray decarb solvent product, such as SeaFoam Deep Creep, is needed to do the decarb process. Free moving rings are what seals your cylinders and gives you compression. Compressed and stuck rings meanss loss of compression, broken rings, and eventually, engine failure.
1)Run engine at fast idle, with engine running and warm, slowly spray liberal amount of decarb spray into each carb. Its gonna smoke up the place - BIG TIME.
Spray for a couple minutes, now spray a larger amount into the carb(s) until engine chokes out and stops.
2)Remove spark plugs and spray the decarb product liberally into each cylinder, install the spark plugs, let it soak for an hour or more.
3)Start the engine and run at medium throttle, or if on the water, run it at full throttle. It won't hurt to spray some more through the carbs. Run it for atleast 10 minutes to flush the crud out of your engine. Now remove and clean, or better yet replace the spark plugs.
It works well to do the spraying, the night before you go on the water. This way you can let it soak overnight, and run at full throttle under load.
Don't do this in front of the garage door or the house, unless you want it covered with greasy black crud.

#3 Ishmael

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Posted December 15 2004 - 7:25 PM

OMC also makes a de-carb spray. Ya spray the whole can in the choke while the engine's running.

#4 makorider

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Posted December 16 2004 - 2:07 PM

Pretty much just as bottomline said. Couple of points though....
As far as adding these types of additives to your fuel tank...which I once tried...if you have an older boat, be careful. It will loosen every bit of sludge and varnish, I was clogging filters left and right for awhile. Now I just shock it.
I use the straight seafoam. Deepcreep is the same thing, just in an aerosol type can. I havn't seen it at my local NAPA, so I just pour the seafoam into two windex bottles and spray by and alternating between the three carbs on my V6's. Do try to bog it out once you start running out of juice.
Pulling the plugs and spraying some in is what I do as well, you may just want to turn the engine over a few times before replacing plugs, trying to compress a liquid is not a good idea, plus you'll get better coverage on your rings.
Seafoam is fast acting (much more so than the OMC stuff). 15-30 minutes soak time is more than enough. Remember, this stuff works from heat, so you want your engine warm when you shock it, and I would think warm when you go to blow it out.
Lastly, be prepared to kill every mosquito for miles downwind. If you've never decarbed before, be ready for your neighbors to be calling the local fire department thinking something is burning big time!! But the smoke is good, thats your carbon buildup going bye-bye.

#5 SS Minnow

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Posted December 16 2004 - 6:47 PM

I decarbed my power ice auger the other day using the procedures described above. When done it was starting easier than ever. A few more days of this weather and I'll be giving a true test run on the lake.