Decarbing might help?

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

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

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

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.

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?

Decarbing is inexpensive and can be beneficial.

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.

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

[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?

Click to expand...

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

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!

That's exactly my plan!

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.

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.....

[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:

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?

Click to expand...

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

Click to expand...

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.

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.

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

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?

What is your idle RPM at?

650 in neutral

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