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I have a 50 HP merc. I see talk on some boards about decarbing and using additives like Seafoam or ring free in their gas. Is this recomended for my motor ?
I had a 35 HP Force for 10 years and all I ever did was change the plugs every 2 years and the lower end fluid every year.
i also had good luck just lettin 'em be. I had a v4 johnson from '79 that i sold in 1998, changed the plugs and the motor always ran like a champ. Consider: what did engine owners do before seafoam was invented? They didnt decarb ill tell ya that much. Plenty of fans of the decarbing but i dont understand the exact principle of it, i never had a motor fail because of carbon deposits. Who knows, im going to stick with what i know, and that plenty of gas and oil and keep running the girl.
I think you will find decarbing is more important with the new technology in outboards to date. Carbon is very abrasive as we all know so I am sure it is not good for any motor.
I just pulled the heads on my 1988 Merc 200 for the first time. I have only had the boat for 4 1/2 years and never decarbed it. Everything looked good. No carbon build up anywhere. I just crack her wide open sometimes to clean her out. The reason I pulled the heads was because the boat mechanic I took it to said Mercs were known for blowing head gaskets. He said to replace them every 5 years. For less then $100 it is cheap insurance in my book. Now for cheap insurance don't get me started
The carbon that will kill you is not the carbon you see, it's the carbon on the rings that over time prevent them from seating correctly and when that happens you get to walk. You can run it wide open all you want but unless you use a fuel additive or a yearly treatment it will happen. I'm only speaking from experiences here. The larger the motor, the more fuel running through it, the faster the build up. Maybe a educated tech will step in here but then again they would be hurting business by doing so.
What you are doing is making a broad ranging statement and trying to make if fit all circumstances. Yes you are right in saying that if the compression ring seizes up because of carbon the engine is in need of a rebuild. But you will not be walking, you will only be blowing blue smoke because of blow by. And it's not really carbon that is causing this, it is more of a residue build up. Rings / cylinders can have other problems other than residue / carbon which will result in blow by and therefore require rebuilding.
Carbon does not have a favorite place to reside (like the rings and piston grooves). If the engine is properly maintained and not driven like Ma Perkins or Pops Walters would drive it, carbon is rarely an issue with the rings when the rest of the Cumbustion Chamber (CC) is in great shape. Angles, corners, ridges and hollows have an effect on how the gases are burnt off in the CC. Flat smooth surfaces gather the most carbon by ten fold. So then if the tops of the piston and the the valve head is clean, worry not about anything else.
So the boat I was riding on that broke a ring (1989 88 HP Johnson) and imbedded chunks of it into the cylinder head was a hoax. The cylinder walls and pistons had marginal carbon build up but the rings and their seats were caked with it. When they got to a point where they could not seat freely, the one in question broke and a perfectly running motor was all of a sudden in need of a partial rebuild. This was on a motor that had never been decarboned. The original question was whether to do it or not. If you were to take a poll of users on this board I would bet 80-90% would vote to use some sort of carbon treatment. I fish year round, run my motor hard and I decarbon. She just turned 17 and runs like a sewing machine.
Garett, you are not correct when you say carbon does not have a favorite place to reside. Modern outboard engines are prone to carbon build up on the lands of the rings. You will not see that when you pull the heads. It is caused by deposits in the combustion process which is unique to 2 stroke motors(although 4 strokes can get it to a lesser degree). The lands will clog from behind and the ring will eventually stick and a peice will break off. Some engines are more suseptible then others and there are many environmental factors but mostly it is the highly refined gas and the 2 stroke oil that is the culprit. Trolling doesn't help either. Considering all the money spent on a rig, a can of tune up once or twice a season is cheap insurance. Pay now or pay latter. You know my dad used to brag that he never changed the oil in his cars and oil changes were over rated. What he didn't realize is that by 50,000 miles he was burning a quart a week so he did in fact change his oil reqularly. My point is.......I forgot what my point is
Kids Stuff,
You're on target. In addition the process is called "coking" One of the major contributors is the additive in gas that causes the rings to stick in the grooves and not expand. When this happens, the piston slaps in the cylinder causing scoring and thus loosing compression. I had it happen to my 155 hp commercial Evinrude the looked like it should have been on the showroom floor. The starboard bank of cylinders had lost compression down to 70# in each cylinder. The dealer couldn't believe it. If I hadn't taken a compression test in the spring I wouldn't have know it until it was too late. Even so I had to rebuild that bank. Do I use a carbon product now? You bet! Even though it's a four stroker. I've talked to baymen who ar running four strokers with 2000 and even 5000 hours on them and they all use ring free and such.
I try to learn something new everyday, well this certainly qualifies. I appreciate the insight guys, thanks.
The wheels are turning and things are set in motion, I've got to find out why this is happening to the larger out board engines and not other 2 strokers? Is it the type of oil? Is it the pressure?
QUESTION:
Basically are all of the engines 115 hp and up running 4 or 3 rings to each piston?
Is it only the number one ring (compression ring) that is having the problems?
On engines with excessive carbon build up, is there an unified amount of carbon build up on the circumference of the #1 ring and groove?
FOOTNOTE:
If the engine I was operating was susceptible to carbon build up, for starters I would be going to a hotter plug to combat that build up.
Garret to answer your question, the reason it is more prevelant in larger motors is because there is exponentially more gas and oil running through them than a smaller 2 stroke. The more that runs through there the more deposits left. Also the smaller motors as a rule get run much less overall time than the largers ones. How often does a 50 HP outboard get taken on a 50 mile run? I have found this topic comes up frequently however, now we are discussing why we have to do it and I find it very informative.
Decarb or not ???
The reason I pulled the heads was because the boat mechanic I took it to said Mercs were known for blowing head gaskets. He said to replace them every 5 years. For less then $100 it is cheap insurance in my book. Now for cheap insurance don't get me started 
