Re: Carbon build up question?
There used be be a post on decarbing in the FAQ, but here is what I found doing a search for decarb:
» 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 should 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, Power Tune, or Ring Free, is needed to do the decarb process. Free moving rings are what seals your cylinders and gives you compression. Compressed and stuck rings means loss of compression, broken rings, damaged pistons and heads, and eventually, engine failure.
Run engine at fast idle, with engine running and warm, slowly spray liberal amount into each carb. Its gonna smoke up the place.
Spray for a couple minutes, now spray a larger amount into the carb(s) until engine chokes out and stops.
Remove spark plugs and spray the decarb product liberally into each cylinder, install the spark plugs, let it soak for an hour or more.
Start the engine and run at medium throttle, or if at the lake, 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 replace the spark plugs.
It works well to do the spraying, the night before you go to the lake. This way you can let it soak overnight, and run at full throttle at the lake.
Don't do this in front of the garage door or the house, unless you want it covered with greasy black crud.
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The following was posted by Dhadley, member #685. It explains the need for doing a decarb as part of your regular maintenance.
""As for the carbon or coking, it all has to do with combustion temps and load in a 2 stroke outboard. We're not talking engine temps, but rather combustion temps. We're talking about an outboard, not a motor with very low and consistant exhaust restrictions like a motorcycle or a snowmobile or even a car.
We're also talking about an engine that is always under a strain. Unlike a motorcycle or snowmobile or a car. An outboard must take off in high gear. Unlike other vehicles that have transmission that keep the motor "happy". Try that with your car. Outboards never coast. Would your car like that?
Thru the years as the fuel changed we have seen this coking problem (carbon build up) get worse and then a bit better. It really seemed to help when the EPA removed MTBE from the fuel.
Anyway, heres the results of some testing we did for OMC back in the mid 80's or so. It remains constant today.
We used a V4 crossflow on a 16' boat. For the first part we loaded the motor up heavily -- dropped the X dimension and used a prop that would only allow a top rpm of 4800 with 2 people on board and 18 gal of gas. When it got light on fuel and only one person it would still only get to about 5200. Extreme? Yes, but it happens. Look on this board how many folks talk about their set up being close to this.
At the time OMC was recommending that Engine Tune be used every 50 hours. We were still seeing coked up pistons and broken rings.
On our test motor we coked up the pistons (starboard bank) in 12 hours of running. We broke rings at 19 1/2 hours.
We rebuilt the motor and set it up on the same boat to turn 5800 with 2 people and 18 gal of fuel. We used no Engine Tune, no Carbon Guard or additives of any kind. Just OMC TCW II (I know, it was old school but thats what they wanted). After 500 hours there were no stuck rings or carbon issues of any kind.
In both parts we ran the boat just as a pleasure boat. Cruising, idling, running flat out -- nothing special. The carbs were always clean, the water pressure was always correct, Champion plugs were always used as well as fresh 87 octane fuel.
Now, if you look at combustion temps with that motor, the temps were much higher in the first test than the second test. High combustion temps promote coking. Coking leads to stuck rings. Eventually the rings break (more correctly the end is sheared off as the piston losses support).
Hope that helps some.""
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And this was added by DJ, member 5471.
""Outboards are probably the most abused engines ever.
An incorrectly propped engine is the norm, not the exception. That incorrect propping results in carbon build up. It has nothing to do with lead.
Think about it. Some folks dole around at trolling speeds or non-planing speeds for hours. That leads to serious deposit build up. Add oil in the fuel and you get the problem described.
Engines that run at high speeds for most of their lives may never have the issue.
However, a decarb does NOT hurt anything, except maybe the plugs, and is a good preventive maintenance practice.
BTW, the decarb. process has nothing to do with gunked up carburetors. That's a fuel storage issue best dealt with using fuel stabilizers.""
