The Boating Forum - How do you "decarb" your 2 stroke??

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Greg Manning
12-15-2003, 08:02 PM
May sound dumb...but this comes up a lot and I have no idea what you guys are talking about. When someone says "they decarb every 6 mo or once a year" or whatever...what procedure are they doing? Greg

12-15-2003, 08:22 PM
Decarbing is the act of getting excess carbon out of your 2 cycle engine. Too much of it can kill your engine (Blown Head, Piston scarring, etc). There are several ways to decarb. One way is to run a concentrated mixure through your fuel system of something like Sea Foam (available at Napa, Carquest and other auto stores.) another way is to buy Mercury, Yamaha, or Evinrude spray and spray it into your carborated engine through the air inlets. Some decarb every 50 to 100 hours I do mine about once a year since I use good quality oils and an additive like Ring free that helps reduce carbon build up in my engine.

12-15-2003, 09:14 PM
Sure today there is all kinds of products on the market for de-carboning an engine; I'm old school, I use water.

It is a lot easier to show one how to use water than it would be to explain. But let my words ring clear, using water one can easily creat bent valves, rap valves off of the tops of pistons, bend rods, pop a holes in the top of pistons, blow heads off of the block and even send pistons through the block wall if done incorrectly. But despite the dangers, I have and will always continue to use good old H2o.

Substantial build up of carbon in any engine is a reason for concern. It is just part of my engine maintainance program and it should be everyones as well.
Merry Christmas to All

12-15-2003, 09:55 PM
One of the purposes of RingFree is to clean the carbs. It's redundant and a waste of time and money to run another treatment for the same thing.

Pursuit 2470 CC, Twin Yam 150's

12-16-2003, 06:28 AM
I use OMC Engine Tuner. Instructions right on can. Every 50 hours or so. Works great. Boston Whaler, "MUMBLER", 24' Outrage, twin 175 HP Evinrude Ocean Pros. Snowball, the cat...

12-16-2003, 07:55 AM
Here's a copy of Dunk's method using Seafoam:

This works for Carbed, EFI, Ficht, HPDI, Optimax and even 4 strokes...
First you need a separate small fuel tank. One of those 3 gal red Tempos works great or an empty gal mike jug will also work, but might be a bit messier..
I use Seafoam over the OEM stuff like OMC Engine Tuner or Merc Power Tune because in the last few years they changed the formula and you have to let them sit up 12 hours. Who's got time for that?? Seafoam you can buy from NAPA, CarQuest or other auto stores. Seafoam works in 15 mins.
You'll need 3/4 gal of gasoline and one 16oz can of seafoam for each engine. Don't forget to add 3oz of oil if you are premixing in a carbed engine. Use about 3 ft piece of fuel hose off the little tank. You connect this tank to your engine by pulling off the main tank fuel hose off the intake side of your water separating fuel filter and plug the hose off the small tank on to that fitting. Or you can separate the fuel line on the tank side primer ball, so you can still use your primer. If you have an engine that has fuel plug then you need a fuel plug on the little tanks hose.
Start the engine, let it warm up and start pulling the mix into the engine. You may have to increase the idle to keep it running once she get loaded with the Seafoam. Run the engine 15 mins in the dock or just cruising around under 2500. Then shut it down and let it sit for 15 mins. Restart the engine, the smoke you see is the carbon burning off. Do the whole thing again and let her sit again for 15 mins. If she smokes after the second time do it again, but I've never seen one still smoke after three doses. The gallon mix should be enough to do this 3 times. You don't need any wide open throttle, you don't need to change the plugs. If it's cleaning the combustion chambers it's also cleaning the plugs, but every 50-60hrs is good time to change plugs in most engines.
I cleaned a antique evinrude one time that had a 1/4" of solid carbon on the exhaust chamber walls by running a 1/2 gal of the mix through it. Seafoam has been around since the 30's and it's what they used when they were burning straight 4 stroke 40SAE oils in outboards.
You guys with the 4 strokes think you are immune from this? Those engines work 10 times as hard as any auto engine ever will and they will carbon up. I bought a Bronco two years ago that had 95,000 miles on it. When I used seafoam on it I had the neighbors hanging out of their front doors looking for where the fire was after I started it the first time there so much smoke.
Too many are under the assumption that it's totally the 2 stroke oil that causes the carbon, Wrong... it's also the additives they put in the fuels today. The carbon inhibitors in 2 stroke oil are there for this reason also. Remember when gasoline used to smell like gasoline, today it smells more like bad cologne.
For those guys that like to do the carbon treatment by spraying it down the carbs Seafoam also comes in spray can called Deep Creep. It's the same stuff under pressure. Says right on the can Oxygen Sensor Safe, for you Yam guys.
After that if your engine maunf recommends a daily additive treatment then do that in the mean time, but all 2 stroke outboard need decarboned every 50-60hrs. If I owned a 4 stroke I would do it the same. Once you are set up with the tank and hose the Seafoam is only 5-6 bucks can. It to easy not to do it.

12-16-2003, 09:22 AM
Decarbing is the act of RUINING yoru motor. Leave it alone already. Add Ringfree as suggested to each tank of gas, use Yamalube oil, and enjoy the long life of your motor.

Ever notice the Yamaha manual DOES NOT state to decarb your motor? There's a good reason for that. Cause ya shouldn't. You do more damage to the motor than good.

Birdman, Capt of
Scout Abaco 280 Click here! (

Greg Manning
12-16-2003, 09:58 AM
Birdman..interesting twist on the topic....this is my first Yamaha after many years of Johnsons....have never decarbed anything to this point and got many hours out of the Johnsons. After reading the board, though, it seemed like something I really should be doing. I may still decarb...who knows. I'll have to read/research some more. Greg

12-16-2003, 10:18 AM
I now have a evinrude 150 FICHT but previously I had a 1989 Yami 200. I never ever decarbed it once in 14 years. The engine has over 1000 hours on it and still runs like it was out of the box. Also it was run on Wal-Mart oil. While I don't run my ficht on anything but the Ficht oil and I do add all the additives I often wonder.... If I had a regualar two stroke I certainly would not decarb her.

12-16-2003, 10:29 AM
Here's some of the skibbes on why someone should decarb.

Carbon adds weight to valves and pistons. That weight reduces response time of the engine. That weight reduces efficence of the engine.
Carbon reduces Horse Power.
Carbon reduces air flow.
Carbon build up is know to cause engine knock and run on.
Carbon build up can give you hot spots. Hot spots on piston tops will give the piston a lean to it, this causes the piston to wear one side of the cyclinder more than the oposite side - in effect, making the bore out of round, oblong if you will. Hot spots have been know to blow holes in tops of pistons.[/list]

How what the the benefits of not decarbing?
Merry Christmas to All

12-16-2003, 11:26 AM
quote:Originally posted by Birdman:
Decarbing is the act of RUINING your motor.

I respectfully, but unequivocally, disagree with that statement.

That said however, I wish no ill will towards the poster, their opinion, nor to their OB, yet I will advise any and all new OB owners to do otherwise.

FWIW this topic - decarbing - has been rehashed many times, check the archives. Truth is, there may be many factors why or why not your specific OB may build-up carbon or it doesn't. These can be your use, duty cycle, interior finish of cast surfaces, porting/jetting, quality of fuel, quality of oil, etc., etc., . Heck, one could run twin OBs and have one load up while the other runs great as is. So the point is ... wouldn't one want to know and possibly prevent a catastrophic incident from occuring ?

For the record, many OEM manuals emphatically state that the OB should be decarbed periodically. I don't know whom Birdy might be quoting, but for me ... I'll go along with the OEM manufacturer's word, plus the opines of Dunk, Seahorse, Sal, and other OB gurus.

Truth is ... your OB needs carbon (cools the rings) ... but not too much. FWIW my brothers and I do the "Dunk" Seafoam treatment, every 50-60 hours, for up to 11 or so OBs that we run each season and we have NEVER had one problem. I've logged 22+ years (running when sold) on OMC engines ... you?

My brother's in law's chainsaw stopped working this Fall, so I emptied the gas tank, added Seafoam and removed the plug wire. Primed it and cranked it through many times, then let it sit overnight. Nest day, we drained the Seafoam and filled up with new oil/gas mix. Started 1st pull ... and hasn't burped once yet.

Seafoam - IMHO cheaper and better than the rest, period. Use Ring-Free, OMC Carbon Guard, or the equivalent if you choose to spend more $4 than you need to . If one chooses to use nothing, that's cool too .

Like many things in boating ... your mileage may vary ... "Life's too short to own an ugly boat ..."


Greg Manning
12-16-2003, 01:03 PM
Reel Rascals...what method..step-by-step do you use to decarb your motors with Seafoam?

12-16-2003, 01:25 PM
I agree with Real Rascal.Decarbizing(?) will definitely help longevity of an outboard.Products like Engine Tuner(omc),Power Tune(merc) is definitely a help.I don't have the answer on the direct injection engines because of the nature of their oiling systems.Oils ,like Quicksilver/Mercury precision Premium Plus has a additive similar to Quickleen(which is Mercury's version of Carbon Guard or Ring free).Three things that can kill an outboard is poor quality of oil(carbon build up),fuel quality(ie alcohol),& improper propeller.

12-16-2003, 02:15 PM
quote:Originally posted by Greg Manning:
What method..step-by-step do you use to decarb your motors with Seafoam?


FWIW I use the "Dunk" method posted above, same as from this link:

Cheers ! "Life's too short to own an ugly boat ..."

12-17-2003, 01:54 AM
I would like to add to my list above.
Carbon can restrict the movement of the rings.
* decrease in compression
* piston slap
* scoring of cyclinder walls
* uneven wear to cyclinder walls
Premature engine failure.[/list]
Merry Christmas to All

12-19-2003, 09:31 PM
Reel Rascal,
To QUOTE YAMAHA, "DO NOT DECARB your Yamaha outboard motor". Quote un-quote. Right from the Yamaha mechanics school.

The reasons (to answer garett's question):
* You ruin and nulify about 6 different sensors including but not limited to the O2 sensor. The sensor's are damaged by two things: The chemical treatment, and the residue left behind that ends up stuck in them.

Remember, if you spray, add, drip, plop or use any other means to put something into your motor, it then has to drip, plop, squirt, or even burn (creating you guessed it, chunks of CARBON) to get out of your motor.

Agian, THIS is the reason Yamaha recomends using Ringfree (a Decarboning agent) in every tankfull of gas. This way your not allowing carbon to build up in the first place.

Birdman, Capt of
Scout Abaco 280 Click here! (

Magothy Boy
12-22-2003, 11:21 AM
I run a Yam 200 HPDI. I decarb using Sea Foam every 50 hours and use Ring Free. Even with RF, I have carbon build up that Sea Foam removes. Use the pup tank, works great and it is easy. Engine runs great.

Grady-White 226

12-22-2003, 11:48 AM
if you use a synthetic 2 cycle oil you dont have to worry about decarbing your outboard as synthetic oil doesnt form carbons

12-22-2003, 12:45 PM
My LAST post on this subject because I don't want to go out of 2003 and start 2004 on the wrong foot and let someone spoil their motor...


Yea! That was a scream. HAPPY HOLIDAYS!

Pursuit 2470 CC, Twin Yam 150's

10-21-2004, 01:55 PM
What if your motors are fouling plugs and blowing out a lot of blue smoke despite using Ring Free and Yamalube. Should one decarb under those circumstances?

10-21-2004, 02:15 PM
My 70 yamaha never made mention of decarbing in the owners manual. I will have to check the Mercs.

10-21-2004, 04:13 PM
I use the WOT brand on my 200 Merc. Another brand I like is 5800RPM. I use either for about the last 10 minutes of each trip and it seems to work for me.

10-21-2004, 04:18 PM
Hey Shag! That's what I use. Works like a champ.

10-21-2004, 04:23 PM
if you use a synthetic 2 cycle oil you dont have to worry about decarbing your outboard as synthetic oil doesnt form carbons

True ... but the fuel still does :roll , carbon is a byproduct of the combustion process and the last time I checked ... yup, fuel was required for it.

10-21-2004, 04:35 PM
Comment On Seafoam:
Since they quit using leaded gasoline the new octane booster has a useful life! During the really hot Texas weather 30 days small quantities of gasoline can go bad and form varnish and plug carbuerator jets and needle and such equipment as lawn mowers, and small gasoline two cycles..ATV's and motorcylcles, etc.. shuting off the gas and running out the the carbs helps...but it still might quit idling properly. I have used that seafoam on the intake of the carbs like the directions and also emptied the bad gasoline and refilled it with a little gas and seafoam mixture and saved many a carb cleaning or trip to the mechanic..Its also good as a gasoline additive for cleaning the fuel system and they also have product for the crankcase....( ) This website list their products and their uses... I learned about them on an ATV board...They store most ATV's through the winter and have problems..
:o :grin:

10-22-2004, 10:18 PM
FWIW, on page 33 of the owners manual for my 2000 Johnson 115 states:

"IMPORTANT - Decarbonize pistons and rings at least annualy using OMC Engine Tuner. Refer to Maintenance Schedule. Allow engine tuner to soak for 8 to 16 hours. Run the engine at fast idle for at least 15 minutes to clear all tuner from the engine."

I have used OMC and Merc, but may try the Dunk method this time. Shadow

Glen E
10-22-2004, 10:46 PM
So what the verdict guys - do I do this seafoam thing on an optimax if I use dfi oil and quikleen on every tank?

10-22-2004, 11:15 PM
I use the SHAG method every trip. from the daymarkers at CALICO JACKS to HARKERS ISLAND FISHING CTR. :grin: Works for me. Also my SUZUKI man SAID DO IT . ;)

10-23-2004, 03:57 AM
BigBone - 10/21/2004 1:55 PM

What if your motors are fouling plugs and blowing out a lot of blue smoke despite using Ring Free and Yamalube. Should one decarb under those circumstances?

Either your running way too rich overall, or your oil mixture's off (too much oil). De-carbonizing isn't your answer until you fix what's causing your problem.

10-23-2004, 04:01 AM
strikerthree - 12/22/2003 11:48 AM

if you use a synthetic 2 cycle oil you dont have to worry about decarbing your outboard as synthetic oil doesnt form carbons

You'll still get carbon, just less of it. I've tore down 2 cycle motors that were run on nothing but synthetic oil and there was still carbon in the combustion chamber. Carbon is a byproduct of fuel burning.

LI Sound Grunt
10-23-2004, 11:03 AM
I decarb my 96 Johnson (carb) via the tuner can direct hook-up method. I think the full throttle operation for a few minutes of every trip is probably all you really need. (I think this is good advice for 4 strokers too)

I do not do anything to the 2001 (direct injected) Rudes.

It was suggested to me that if you do do it, do it in the spring and not as part of winterization as it will dry out much of the lubrication you may want during winter storage.

10-23-2004, 11:37 AM
Check out this little experiment I did.
I picked up a neat 13 Whaler for the bays with a 1994 40 Merc, the owner before me wasnt very good @ keeping it clean allthough the engine is fine & hull is sound.
I got into cleaning the heck out of it, compound, wax, touch up paint on motor, everything..
The motor had carbon buildup on the lower unit as many do, like a coating of carbon underneath the exhaust ports on the outside of the LU below the case.
Anyway in my pursuit of detailing my new toy, I poured some Ring Free on a rag & went @ the carbon rubbing it real hard & to my suprise little if not any of the carbon came off.
A couple weeks later after purchasing some Mercury Power Tune I decided to give that stuff a try on the carbon buildup & took it off sooo quickly & easily, it just cut through this carbon to the nice black paint underneath , I was amazed .. :)
I guess the Ring Free works slowly but I believe Ring Free alone may not be enough & my decarb regimen for this motor's going to be Mercury Power Tune spray in stuff once every 50 hrs. or so & no Ring Free after witnessing this..
I bet the OMC power tune is just as good I used that with my OMC motors in the past & the trick is to let it soak @ least an hour then clean the plugs, also I use the power Tune to clean plugs with, it dissolves the carbon that stuff, like magic Mon ! ;cool;

Glen E
10-23-2004, 01:09 PM
Nimrod -

Ok - I did it - after 500 trouble free hours of DFI oil and quikleen - I took your advice and "went under the cowl" on my Opti's- which I do not like to do. It went just as your said, but the only thing that surprised me was after two 15 minute sessions on each engine - I went thru less mix in the millk jug than I thought I would - maybe 3/8 of a gallon of the 50-50 mix of seafoam and gas. I ran the engines at about 900 rpm. Also, I got very little smoke after starting back up and running. However it did have an effect. In a quick hour run down the intercoastal in which you can go WOT for a few miles or so, I am running 2 degrees cooler at idle and WOT. Thanks!
Any advise?

10-23-2004, 02:16 PM
gersly did you change plugs afterward? I bet if you would notice a different attitude at idle.

Glen E
10-23-2004, 02:24 PM
no I did not change anything as I just put in new plugs at the 100 hour check that was done two weeks ago - what do you mean "attutude"? - the engines seem to run smoother and idle is perfect...

10-23-2004, 02:44 PM
After I decarb and change plugs the idle becomes smoother than it was before.

Glen E
10-23-2004, 03:05 PM
well seeing as I just changed and they are about 6 bucks apiece..I'll have to wait...thx...

10-26-2004, 12:18 PM
Sure glad I seen this thread last week....I was down washing my broke a$$ SeaCraft since it had been stored outside while jerked me around for 9 months.... whoops sorry...any way my brother-in-law was towed back to the dock and I checked his spark plugs which he said had never been changed (early 90's model wonder he needed a tow). So I ask him to run into town to buy a set of plugs and get a can of sea foam. The spark plugs helped, but the sea foam was what it really needed.

Afterwards he said it has never ran that good....EVER!

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