Decarbon, fact or myth

[scofflaw]

In my 40 plus years of running 2 stroke engines I have never decarboned or had a carbon related failure. Maybe someone can enlighten me of why you are getting a carbon buildup if everything is jetted correctly. I do say that all my outings have a fair amount of WOT.

[boscoe99]

When hydrocarbons (gasoline or oil) are burned, at any air/fuel ratio, they leave deposits behind. AKA carbon. That's what they do.

When I had my Mercury EFI I would decarbon it yearly using Seafoam and what is referred to as the Dunk method. Motor would have about two hundred hours time on it. First time I started it up it smoked like hell. With each subsequent start up it smoked less. Finally it did not smoke at all. Led me to believe it was the carbon being removed by the Seafoam was the stuff that was smoking.

99.9% of people that have a motor will more than likely never have a carbon related problem. It is the 0.1% that they are trying to reach with additives and decarbon procedures.

[ausnoelm]

I find it strange that cars, lawn mowers, chainsaws and all sorts of equipment run for decades without the need to run anything in them to decarbon them, yet these days, outboards need to be done to fix everything, and if you don't, then your motor will surely blow up. Now that said, I am not saying it should not be done, and might be good maintenance, but there is a lot of marketing hype too.

[99yam40]

I have only come across 1 2 stroke motor that had stuck rings from carbon.

It was a leaf blower that looked brand new.
belonged to a friends son. said he had only run it for one summer/fall before he could not start it anymore.

Compression was too low for it to start and run.
I took it apart and removed the rings to clean them and the grooves out. put it all back together after manually cleaning all of the carbon out or the ring grooves and it runs like new now and have very good compression.
I did not put anything new in it, just cleaned every thing up,

when I ran seafoam shock treatment in my C40 when I 1st got my hands on it used it smoked very bad at 1st , and tapered off.
Had black goo run out the prop exhaust while sitting in drive way after that, so it had to be some of that carbon as black and thick as it was

[boscoe99]

I find it strange that cars, lawn mowers, chainsaws and all sorts of equipment run for decades without the need to run anything in them to decarbon them, yet these days, outboards need to be done to fix everything, and if you don't, then your motor will surely blow up. Now that said, I am not saying it should not be done, and might be good maintenance, but there is a lot of marketing hype too.

First let me say that I agree wholeheartedly with the comment about the marketing hype. But let's look at it from Yamaha's position. If they can convince folks to use their additives there is no down side for Yamaha. Only profit to be made. And in so making that profit they might have reduced just a bit their risk of someone having a damaged motor, that Yamaha would be expected to repair. It is a win win for Yamaha. Maybe a big win for the one customer and wins for the thousands of users who did not have a carbon related problem but who feel better about their motors. That is also a win for Yamaha.

Having said that, outboard motors run considerably cooler than do automobile engines. That brings about a different set of issues. Now let's take a look at air plane piston motors that run considerably hotter than do automobile engines. That brings about a different set of issues. Both can, not will, cause carbon problems.

And finally I agree with your comment that cars, lawn mowers, chainsaws et al can run forever without nary a problem without ever seeing a drop of decarboning additives or actually being decarboned. I have owned all of the above for over 50 years and never personally have had any carbon related problems.

Now I will finish by saying that when I worked for Yamaha I saw it all. Carbon and other buildup like one would never believe. Red sticky goo holding valves open. God only knows how some folks run their motors, and on what.

I suppose carbon additives are a bit like insurance. The vast majority of us will never need either. Some have insurance and some use additives just to be on the safe side. Or to have a certain comfort level. Through at 10 new cars and trucks over the past 50 years I have never spent a dime on comprehensive (fire and theft) insurance. I took my chances. For me it paid off. For some it might not have.

[boscoe99]

Fuel additives may be a bit like vitimines. We take them and don't feel badly so we think they must be good for us. But then, maybe they are. Or maybe they are not good but don't hurt.

Might be psychosomatic but my knees hurt (only when I walk) so I started taking some stuff for them. My knees feel better. Or rather they don't hurt as much. Is it my knees or is it my brain that has been made to feel better?

[rodbolt17]

I don't use ring free.
I do a yearly dose of either combustion chamber cleaner or yamaha's YIES cleaner.

that YIES is magic juice.

I have taken engines with 85% leakage and made them go to less than 10%.

[Nautical]

I think carbon was more a factor during the leaded fuel days when you needed to do a hard hot run to remove the lead build up aka as carbon. Todays fuels are advanced and require detergents in the formula due to fuel injection and emissions. Actually alcohol is a very good cleaner .. You should see much less carbon build up in todays' engines if you use a good quality fuel or if you add your own detergents as a supplement. Still will be some carmalization when the spray hits a hot intake valve, but much less than days of old.

[99yam40]

Seems I have read YIES cleaner is not available to the general public for use, only dealer use

Think of the carbon build up when the old 2 stokes used regular old 30 weight motor oil in the mix instead of the high quality 2 stroke oil they out there today .
I have had and still own some old Sears Craftsman chain saws that called for 16 to 1 mix of gas to oil. Yes they needed to be decarboned from time to time

[Zara Spook]

Here's a related question: would folks feel comfortable putting an appropriate (i.e., relatively small) amount of an additive such as Seafoam into the crankcase oil of a four-stroke engine?

[TownsendsFJR1300]

Here's a related question: would folks feel comfortable putting an appropriate (i.e., relatively small) amount of an additive such as Seafoam into the crankcase oil of a four-stroke engine?

Its designed for the crankcase too and I have ran it in mower crankcases just to help keep the rings free with the help of the engine oil (cleaning from below the rings.)



As 99yam posted, I was given a weed-eater that ran, but crappy. Compression (2 stroke) was about 125. I had the exact same machine and compression was 195. Pulled the head/cylinder (one unit) and the rings were carboned up bad.

Had a parts motor and just swapped the piston/rings and cylinder. Runs like a top now.


Another "carbon issue" I had. A Kawasaki motorcycle, 250cc 4 stroke, single cylinder, 4 valves (daily driver), water cooled.

With time/mileage, I was eventually having troubles getting over a local bridge (never was an issue before). I eventually found the issue. A leaking intake valve seal. Oil seeped down into the intake tract, and carbon built up on that valve stem. Probably 1/4" all around the valve stem hampering flow, obviously big time. Valve job time, ran great again after that.

[boscoe99]

Here's a related question: would folks feel comfortable putting an appropriate (i.e., relatively small) amount of an additive such as Seafoam into the crankcase oil of a four-stroke engine?

Most of the carbon buildup I am familiar with is not in the crankcase but on the other side of the piston. On the rings, top of the piston, valves, etc. Then too some deposits appear on the side of the intake valves that are on the fresh air side where they only see gasoline and air.

Most additives won't hurt a thing. If they make a boater feel better then beautiful. Like taking a daily low dose aspirin to try and prevent a blood clot or heart attack. They might actually help a few by preventing negatives from happening and they might help many just by making them feel better.

My dearly departed mom always worked on the theory that if any number of prescribed pills were good, then even more were better.

[Nautical]

I recently replaced the heads on a chevy 5.3 V8 with 195,000 miles. No issues , maybe some valve seal oil leakage at start but great running..Just got the heads new on a deal and felt it was time. FYI the old heads were immaculate..I was amazed that there was virtually no carbon on the valves and just a little on the piston crowns. The owner never did anything to the engine but regular oil changes .. I could only attribute it to the fuels used today and the additives and the hotter temps I guess.

[TownsendsFJR1300]

I recently replaced the heads on a chevy 5.3 V8 with 195,000 miles. No issues , maybe some valve seal oil leakage at start but great running..Just got the heads new on a deal and felt it was time. FYI the old heads were immaculate..I was amazed that there was virtually no carbon on the valves and just a little on the piston crowns. The owner never did anything to the engine but regular oil changes .. I could only attribute it to the fuels used today and the additives and the hotter temps I guess.

The fuel would definitely help BUT today's engines are not like the 60's and 70's, 80's when a valve job was mandatory at roughly 80,000 miles. They ran rich, cooler- carbon easier to build up(160-180 thermostats), simple engines.

Nowadays, with fuel injection, computers, knock sensors, hotter running temps-more efficient, (the EPA), manufactures get the engines to run as clean (on the lean side-not rich) as possible, thus less carbon deposits.

The above is NOT taking into account a leaky valve seal which would cause carbon issues...

[rodbolt17]

some years back,about 1996.
a friend of mine decided to lap the reed box's on his 1985 120 evinrude.
I warned him about loc titeing ALL the reed screws.
he missed on on #3 cyl.
in the course of replacing #3 we did the rings on the other 3 cylinders.
I had to carefully beat all the rings out due to carbon.
all the rings had stuck.

so yep, rings can and do stick.

on a 4 stroke they can also rotate and line up the ring gaps.