Low compression in two cylinders in outboard that has been sitting

[calderp]

I just picked up a boat for almost nothing that has been sitting for an unknown amount of time. The motor is a 1983 Evinrude 115HP. Looks very clean seems maintained but a compression test gives me around 75 on two of the cylinders with the other two about 105. I can see a fair bit of carbon on the piston heads through the plug holes.
Any recommendations? Should I try to soak and de-carbon the piston heads/rings? Should I just try to get it running and crank it at WOT for a few minutes and see if it frees up the rings? Do I need to pull the head? For what I paid and the overall condition if I have to rebuild the motor I will but I would really like to get it running as is.

 

[calderp]

Also if I do have to rebuild does anyone know the procedure on these engines? I didn't see a cylinder rebuild kit in the parts list. I thought most outboards were sleeved cylinders but I'm not sure if this one is or not. Would I bore it and get oversize rings like a car engine? Motor is a

E115TLCTE​

 

[ThomW]

I would say its is worth spraying some cleaner in the two cylinders that are low. Let it soak a few hours, turn the fly wheel to move the pistons a bit, spray again and let sit. Maybe you will get lucky and the rings are just stuck causing low compression. Always worth a shot.

 

[GA_Boater]

Should I just try to get it running and crank it at WOT for a few minutes and see if it frees up the rings? ..............I will but I would really like to get it running as is.

Welcome aboard.

You really want to blow the motor, don't you?

Spray some pre-mix in each cylinder and crank the motor over a few times to lube the walls, rings and pistons. Then check for spark and compression. The compression may have changed, but in any case try to start the motor. If it starts, only let it run at a fast idle on muffs or in a barrel. After warming up, check the compression again. After warming up and running awhile, rings may be freer if that was the problem.

If none of this helps, come on back and ask more questions.

 

[calderp]

Welcome aboard.

You really want to blow the motor, don't you?

Spray some pre-mix in each cylinder and crank the motor over a few times to lube the walls, rings and pistons. Then check for spark and compression. The compression may have changed, but in any case try to start the motor. If it starts, only let it run at a fast idle on muffs or in a barrel. After warming up, check the compression again. After warming up and running awhile, rings may be freer if that was the problem.

If none of this helps, come on back and ask more questions.

Hah, fair enough. I should have mentioned I did check to be sure it wasn't frozen and then I lubed the cylinders before compression testing. I'm going to pull the lower unit before I run it, for all I know the impeller is 20 years old I don't want to risk it disintegrating into the water jacket. Then I'll run it on hose pressure straight up the pickup tube. You think a high idle is best to try to break the rings loose? I guess I thought running it under load was important, if it fired up ok I was going to put in a new water pump and launch it so I could put some resistance on the prop but if I can do it on the bench that's much better

 

[racerone]

Stop.----Remove bypass covers ( side of block ) and inspect pistons / rings on low compression cylinders.----Likely you will find broken rings.

 

[calderp]

Stop.----Remove bypass covers ( side of block ) and inspect pistons / rings on low compression cylinders.----Likely you will find broken rings.

Oh cool I didn't know that was a thing. Messed with plenty motors but I'm not an outboard guy. So there's a cover plate I can pull that will allow me to see the rings without dismantling the powerhead? Seems almost too good to be true. And it's just a gasket replacement to put it back? Thanks for your help!