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There are countless threads on using products to remove carbon from your engine but I have found an interesting contradiction.

Referring to OMC motors;
- The OMC Engine Tuner Product label states that you should leave the product in the motor for 3-16 hours before completely removing it.
-The Johnson/Evinrude official factory service manual states that you should never leave a tuner product in the engine for more than 1 hour.

Which would you follow?

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Good question. I have noticed the same. I recently had my engine serviced by a Johnson certified "master" tech and he said 3 hours. I recently bought a 17 whaler with an 1985 Johnson. He highly reccommends it.
I have yet to decarb - I am concerned my neighbors may call the fire dept... I will try while out at sea. Any other reccommendation on this process and what to expect?

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Expect a lot of smoke, and it might be better to try it off the water to avoid someone claiming you are adding pollutants to the water. I live in CA too and I know it raises eyebrows when my older two stroke starts and belches that classic cold start blue smoke in the mornings! Have a set of new plugs handy just in case, and in fact pull yours before decarbing and compare them. I do mine with seafoam every 50-60 hours and it takes 3-4 rounds of addiing, sitting and burning before it comes out really clean IMO.

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Mr T. do you de carb at home, the dock or at sea? I am thinking at sea. It will definately raise eyebrows in town.....

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I decarb at home in the backyard. I do warn the neighbors, and it is not an issue to this point.

Lot of mechanics in the neighborhood, so no one gets too bent out of shape.

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I've tried a lot of the currently availabel advertised engine de-carbonizing products by actually soaking heavily carbonized pistons in them for hours and even days. Not one of them removed a bit of the carbon. Yes some of the fuel varnishing did come off but not one bit of carbon. So how they work when just running them through the engine...? Just more snake oil as far as I'm concerned.

Sea Foam was one my dad stood by. Its crap for removing real carbon deposits even after more than a week soaking.

I have found a product that does work well when doing an engine break down but its intended for restaurant equipment and VERY caustic. Aluminum parts beware.

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JonnyCW, are you saying you soak the parts removed from the engine and nothing happens?

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Nothing to the carbon. There are other deposits on the parts that will dissolve but actual carbon buildup requires mechanical removal or very harsh chemicals.

We're suckers for the pour-it-in-your-tank solutions to a variety if engine problems but its mostly all crap.

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Well, it sure blew the carbon out of my engine. This was after pouring directely into the cylinders and letting it sit.

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X2....

I used Ring Free in my gas and wow, it made a difference for sure. This might be "Snake oil" but that "snake oil" worked great in my boat.

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If you feel confident with any mechanic in a bottle product, then by all means use it.

I've done my own testing with parts on the bench and I know the manufacturer claims of all the products I tried are way overstated.

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I promise I'm not trying to argue here...just stating that this stuff did indeed work for my application. And yes, of course the manufacturers claims are always overstated....just part of their marketing strategy.

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I don't see it as any kind of arguing. Everyone's personal experience is valuable. If I can soak a carbon encrusted piston for weeks in Sea Foam and it doesn't touch the carbon, I see no way its effective running through the engine. Coked oil in the ring grooves and fuel varnishing are pretty easily flushed but carbon is a rock hard and very abrasive substance that resists even mechanical removal.

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Based on your test results, I can understand your skepticism. But keep in mind that your process doesn't include the steps of igniting the Sea Foam and moving the pistons back and forth at high speed (i.e. starting up the engine after a good soak). That could make the difference. I agree that most of the carbon removal products out don't work, but I tend to believe that Sea Foam works. Mechanics used to de-carbon engines by spraying a light mist of water into the air intake.

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The water caused thermal fracturing of the carbon which could knock some loose. Unfortunately sometimes when it worked, you got chunks of carbon getting tossed around in the cylinder breaking rings and scoring the cylinder walls. Imagine tossing a couple of tiny pebbles into a cylinder through a spark plug hole then firing the engine up. I don't know of any professionally trained and certified mechanic that would do such a thing and if I did, they certainly wouldn't be working on my engines.

FYI for those that may have not already known, the formulation of Sea Foam is actually pretty simple composed of a light oil, naphtha, and isopropyl alcohol.

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Ding, Ding, Ding! Winner, Winner, Winner!

If you've used oil that built up a lot of carbon, better hope that it stays Stuck where it is. I've personally seen 2 stroke ob's blow when someone changed the oil (from a Hi-Carbon Cheap oil) to a better (cleaning) oil. When it breaks loose it looks like someone threw a hand full of sand in the cylinder it gets sucked into. You "might" be able to clean some of it out of the cylinders with the Snake-Oil but inside the engine case, I think No. This is the main reason I wouldn't suggest changing oils. If you bought a used motor and they'd been using $1.98 Brand-X oil, I'd cringe and keep using it.