# Decarbing might help?



## PatinIdaho (Aug 24, 2014)

Have a 83 50Hp merc after getting the carb issues sorted out the engine runs pretty good actually
Problem is the compression is low. Between 85 and 90psi on all cylinders 
Think decarbing the engine might help the compression?
Im almost positive it has never been done and the PO had the idle needles way rich trying to compensate for the messed up carbs. No idea how long it was like that before I got it but its all fixed and adjusted properly by a dealer. I hope!
If decarbing will not do it I guess i'll need to re ring it. From looking at it, it seems like it would be pretty easy as long as nothing else is bad.
The engine is actually in great shape with New stator, Switch box, new seals in LU, Rebuilt carbs with new floats, Timed and Linc and sync, New wiring harness, New prop.
Also if this is going to run over 500/600 bucks I think I would be better off finding a different engine?

Anyone care offer your advice on this situation


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## Natedog57 (Aug 24, 2014)

What negative effects are you experiencing that you attribute to low compression?

If it runs good, with how the carbs are currently set... I would have to think that any adjustments/changes will only have a negative affect on how the engine runs.

Just some thoughts:
1) all compression testers read different values (some quite different), try another tester (or 2)
2) I've always been told 75lbs (or lower) is about time to consider repair
3) a re-ring job will cost substantially more than $500... at least where I am and shops get $75-$100/hr labor


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## Steve A W (Aug 24, 2014)

A good dose of seafoam cant hurt.
I used it on an old 5.5 Johnson and the compression
went from 65 to 90 after a couple of tanks of gas.
Results may vary, no guarantees.
Good Luck with Your motor.

Steve A W


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## PatinIdaho (Aug 24, 2014)

The ring job I can do my self im pretty sure so just parts cost.
Maybe ill barrow a compression tester and check it my self also.

I just got back from the lake and the only problem is this.
Idles out of gear fine. Put in gear and it slowly, slows and dies. I don't believe its loading up but I guess it could be and it also seems to have a couple flat spots. Just off idle and about 1/2 throttle.
From idle to WOT (holeshot)is perfect no hesitation at all.


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## JoshKeller (Aug 24, 2014)

Ive had plenty of OMC motors that were 85 - 90 psi and were strong. I rebuilt a v4 and it was 105 with a fresh bore hone and ring. As long as it runs good, i wouldnt worry about the numbers as long as they are close. Are you testing with the throttle wide open and a fully charged battery?


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## lckstckn2smknbrls (Aug 24, 2014)

Decarbing is inexpensive and can be beneficial.


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## PatinIdaho (Aug 24, 2014)

It was tested properly. I helped I made sure the throttle was WOT and yes it has a fully charged battery.
I am going to try decarbing tomorrow after work. Im sure it has never been done so probably needs it anyway.


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## Charger25 (Aug 25, 2014)

I had a motor just like that on a 17' Tracker. I knew the PO and knew he did A LOT of trolling. The way I did the de-carb was to add a whole can of seafoam to 1 gal of fuel mix. (w/abit extra oil). I let the engine idle for about 10 to 15 min. shut it off for about 5 to 7 min while it was shut off you would not believe the tar and crud that dripped out of the exhaust. 
Repeated this over and over till all of the fuel was used. Then changed plugs, put it in the river and ran it hard. After that ,it started easier and idled smoother. Just my .02


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## earl60446 (Aug 25, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=364338#p364338 said:


> JoshKeller » Yesterday, 18:21[/url]"]Ive had plenty of OMC motors that were 85 - 90 psi and were strong. I rebuilt a v4 and it was 105 with a fresh bore hone and ring. As long as it runs good, i wouldnt worry about the numbers as long as they are close. Are you testing with the throttle wide open and a fully charged battery?



Why the WOT? Not trying to be a smartass, just don"t know. I guess a fully charged battery so it turns over fast. While I am at it, what is the proper way to check compression on outboard. Actually on my johnson, I cant have WOT unless it is in gear.
Tim


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## SumDumGuy (Aug 25, 2014)

Do a decarb with Seafoam. It is cheap, fun and wont hurt your numbers. I enjoy doing it.

I like to run the engine for a while to let it heat up and then start spraying seafoam into the carb until it starts to smoke, cough and sputter then spray it hard until it stalls and dies. Let it sit for somewhere around 15 minutes, fire it up and enjoy.
After I do this for a few times I'll run a heavier mix in the fuel a couple times, then switch to Seafoam maintenance mix.

Good times!


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## PatinIdaho (Aug 25, 2014)

That's exactly my plan!


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## PatinIdaho (Aug 25, 2014)

Well decarbed it but really not Mutch crid came out. Lotsa smoke through. 
Let it run until it cleared some, maybe 10 minutes then the wife started complaining so I turned it off.
We will see if that helped anything Wednesday when I can get to the lake.


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## turbotodd (Aug 26, 2014)

Only way a decarb helps is if the rings are STUCK to the piston due to excess carbon buildup. Yamaha makes a product called Ringfree that will remove 99.9% of it. Only thing that I've found that actually works. They also make another product that is specifically designed for a LOT of hard buildup carbon, that works faster than ringfree....or anything else I've found for that matter....it is called YIEC (Yamaha internal engien cleaner). That stuff is bad. But expensive and makes a huge mess. And requires special handling while using.....


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## JMichael (Aug 27, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=364391#p364391 said:


> earl60446 » 25 Aug 2014, 08:42[/url]"]
> 
> 
> [url=https://www.tinboats.net/forum/viewtopic.php?p=364338#p364338 said:
> ...


If you restrict the amount/volume of air allowed into the cylinder, you also restrict the amount of compression you will get. Always set the throttle to wide open or remove the carb so you get max air flow into the cyl when doing a compression test.


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## PatinIdaho (Aug 28, 2014)

So after taking it to the lake the only difference I noticed was a slightly better idle but nothing to wright home about.
I have some seafoam mixed with the fuel also.


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## JoshKeller (Aug 28, 2014)

honestly, if it runs good, I wouldnt worry too much about the numbers, just that they are close to each other.


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## PatinIdaho (Aug 28, 2014)

That's true but at what point is compression to low to idle? Seems to me that once compression reaches a certain point it will not be able to create enough vacuum to suck in enough fuel/air to even run and I _think _im close to that but maybe im just paranoid.

As I said my engine seems to run fine but when it is warm/cold it will slow and die at idle in neutral or in gear at about the same rate. I, pretty sure it is not to rich and from what I read im certain its not to lean.
From cold it starts right up with just a touch of the choke and once warm it starts right up but slowly, slows and dies after about 30seconds 
When it was timed I was standing right there and it was right on so I don't think that's it either.

Do you have any suggestions to try or check?


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## midwesthunter (Aug 29, 2014)

What is your idle RPM at?


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## PatinIdaho (Aug 29, 2014)

650 in neutral


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## Pappy (Aug 29, 2014)

That engine should probably be around 750-800 RPM in gear at idle at this stage of its service life.


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## PatinIdaho (Aug 29, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=364859#p364859 said:


> Pappy » 29 Aug 2014, 15:22[/url]"]That engine should probably be around 750-800 RPM in gear at idle at this stage of its service life.



So Pappy, After reading several of your posts over the last few months I have grown to respect your opinion so im going to ask you directly.
Im pretty mechanically inclined. I grew up in the Auto/Semi repair business and now in the aircraft repair (Mechanic) and after taking a close look at it I believe rebuilding this engine is well within my capabilities so with that said.

How far do you think it would be feasible to go with this engine work/money wise? 
Would you just run the piss outta it till it died and find another sub $1000 engine? Or fix it up and keep it?

I can't afford a new engine and probably never will. I could sell this one but the next one might have problems also that do not show up right away like this one.

Just rings and gaskets are about $300ish with $100 for odds and ends so $400 total or very close to it
New oversize pistons(rings included with pistons) and gaskets are close to $500 Having it bored probably $100ish so roughly $600 with the little few pieces not mentioned im thinking a total of $700 and if I needed all new bearings that's another $150ish
With just rings I think it would be good for 3 or 4 years at least
With a major rebuild I think it should last about the rest of my life(im 52)
The engine is actually in really good shape and does not show its age. Paint is still bright and shiny. Lower unit works properly and the oil in it is clean.
It has a new Stator and Switch box. Stickers are a little rough but with new stickers it would look almost new.


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## Pappy (Aug 29, 2014)

Have watched this thread to see which way it was going to go.
Your earlier comment/question on how low can compression go before you cant get the fuel air charge to the top of the piston was right on, hence the reply.
A two stroke engine has to have two kinds of compression to idle well. 
It has to have the measured compression we see above the rings and it also has to have adequate crankcase compression/vacuum below the rings to pull in and push or accelerate the fuel charge through the crankcase and over the top of the piston.
Piston and cylinder wear in a two stroke is similar (in most cases) to that you would see in your profession in that the piston skirts will wear at a higher rate than above the piston ring. 
The cylinder will also wear more down in the skirt area than at the top of the cylinder giving you a measurable taper. 
This type of wear translates into a weaker than normal crankcase compression ratio which can and will result in the scenario you were thinking about. 
Your choice in rebuilding would be to over bore and use new pistons and rings, not re-ring. 
Having said this I would definitely raise your idle rpm way before going to the trouble and expense of a rebuild. 
Am not as familiar with that particular engine as I am the Johnson and Evinrude brands but have been around them. Have seen this scenario several times in the 2 & 3 cylinder loop charged engines that OMC manufactured. Top compression would be great but the engine would just "go to sleep" at an idle in gear in the water. 
Band-aids are to raise the idle, richen the mixture and advance the timing to buy some time. 
In your case I think simply raising the idle RPM will help quite a lot since a 650 RPM in neutral would most likely translate into a 500 RPM in gear number...too low.
BTW - My Dad had his "A&E" license issued to him back in the 1940s and I got my "A&P" license in 1972 while going to college in Daytona for Pilots licenses and Aeronautical Sciences.


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## Pappy (Aug 29, 2014)

...on the subject of "De-carboning"
Have seen all kinds of responses on here about what to use and how to do it. 
If you want to do it right get a manufacturers brand first off. They are more powerful.
Second. Bring the engine to temp and on an engine like yours use at least over a half can to as much as a full can. Keep the engine 
running at a high enough idle to not die. It should be running pig rich and barely running while you are using it. Neighbors should think
your house is on fire with as much smoke as it will produce......
Once almost done with the can drown the engine with it, do not let the engine clear out. 
Let the engine sit anywhere between 3-16 hours minimum. I do overnight as a rule. Let the chemical work!
Start the engine and let it sit at a dead idle for at least 15 minutes to clear carbon chunks out. This stuff can scuff the bore as it is
being released so idle only for a while. Add oil to your mixture in a tank you run the engine on to keep the bore as protected as possible after a de carbon job.


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## PatinIdaho (Aug 29, 2014)

Thanks Pappy.
Im leaning towards a complete rebuild. 
For the money I _don't_ think I can find a better deal then I would end up with if I do a major overhaul.
Other then a unknown fatigue issue a engine that is rebuilt should last just as long as a new engine in my experience but 2 strokes outboards are new territory for me! so I guess I have been leaning that way from the start just afraid to admit it #-o 
In a couple months I will be putting it away for 5-6 months(winter) so ill have plenty of time to do it.


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## Pappy (Aug 29, 2014)

Well....in the mean time give the engine around an 800 RPM in-gear idle and see what happens.


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