Johnson 1988 48HP SPL J48ESLCCC compression test

[Sdominick]

Did a compression test on my Johnson 1988 48HP SPL J48ESLCCC , 145 Upper cylinder and 125 lower cylinder.. Good/Bad? I was hoping to have them a little closer together. Its is right at the 20psi tolerance difference. Any knowledge would be helpful. I have fuel spitting from the #36 low idle jet on the upper cylinder. I have the carb rebuild kits for both and I will inspect the reeds while I have them off. If I had a problem with the reeds would that affect the compression of the cylinder as well. Just a question. Thanks for your time.

 

[racerone]

The reed valves have nothing to do with compression in the cylinders !!-----Pull the cylinder head for inspection of cylinder walls and head gasket.

 

[Sdominick]

I understand, 2 separate issues, sorry if I was not clear. Have gas spitting out of upper carb thru the #36 low idle jet. It had been suggested that it could be a reed issue allowing some blow back.and while I had the carbs off i should inspect the reeds. I also had a suggestion that it could be a scored piston so hence the compression test. Inspection of walls and head gasket is the next step. Thanks for your input.

 

[Sdominick]

If a reed was damaged or bent and you did a compression test would it not allow pressure to escape out thru the reed to the carb. Just a question.

 

[racerone]

No it would not !-----The reeds have nothing to do with compression in the cylinder.-------The reed valves have to do with compression in the crankcase.----Understanding how these motors work makes the trouble shooting easier.

 

[Sdominick]

Understood. Again, I appreciate your advice, I little less use of dashes and exclamation points would be helpful. I'm trying to learn and ask for advice, I thought that's what this site was about. I'm an electrical engineer and a diesel mechanic so I can figure out things pretty quick. Supreme Mariner!!!!

 

[juno pierrat]

i'v got a 87' 48, i haven't run with the air silencer off in a while, but i seem to remember a little spitting from carbs is normal, i'm only a Cadet could be wrong, there is a drain to the block at bottom of silencer. as for compression, yap need to inspect cylinder, hopefully just a bad head gasket. as for the dashes and exclamation points that just the way racerone types/talks, he's one of the old guys here , it is what it is

 

[racerone]

Good luck with your project.----Sometimes folks do not like straight forward factual advice.----See post #2 and act on it.

 

[Sdominick]

Update to this post, Upper cylinder 150PSI Lower 125PSI . Thought the problem was with the lower cylinder. Wrong. Sprayed Seafoam in the cylinders for 2 days just rotating the power head by hand (no plugs) working it in. Blew out all liquid by cranking did compression test again both cylinders are a solid 125 PSI. dead balls on. SOOO the 150PSI was over compression? Upper cylinder (150PSI) is the cylinder with carb and back spitting issues. sorta makes sense. Stuck ring? Carbon issue? Before the process, Pulled plug from upper(150PSI) nasty black lots of wet on plug. Lower plug (125PSI) dry and clean/ Now I feel comfortable with the rest of the rebuild knowing that that a cylinder is not shot. When rebuilding carbs i will check reeds. Also have sluffed off carb cam roller that needs fixing. I also would like to thank everyone for their input and advice. Every bit of knowledge from this vast array of people and experiences is important and it is what makes this site so successful. I apologize for my low patience level, the German in me just want straight forward answers to maybe not that straight forward question. I will do better on my part, Thanks again to everyone for helping me. God bless.

 

[Sdominick]

To racerone, I get straight forward actual advice everyday and act on it accordingly, and what I've consistently found, is that information that is delivered in a NON "condescending" or a "know it all" attitude is much more readily received and tends to have better outcomes when it comes to team building and better outcomes to projects with difficult issues. On top of that it looks likes your vast experience was wrong, and the "KISS" method might have been over looked. So you would have me remove the head and inspect cylinders and pistons for something that could be fixed with a spray can and soaking and a little heat? Remember first thing is first. Keep It Simple Stupid!

 

[racerone]

Good luck with your project !

 

[Sdominick]

Looking forward to your advice in future>

 

[oldboat1]

Before pulling off and disassembling carbs, take off the intake manifold for access to the jets at the top and bottoms of the carbs. Spray carb spray into the jets a couple of times, and see if that helps.

When it comes to cleaning, disassemble and soak in solvent strong enough to cut through dried fuel. Then blow out every opening with carb cleaner, and reassemble with the carb kits.

 

[Sdominick]

Thank you.