Low Hour Evinrude 25 Hp Compression Test
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- čas přidán 2. 03. 2019
- Cylinder compression test of a low hour Johnson Evinrude 25 Hp Outboard Boat Motor
An outboard has good compression if the values are above (roughly) 70 psi and are EVEN. By even I mean that the compression values are within 10 psi of each other. Say you tested one cylinder at 100 psi and the other at 80 psi. That’s bad because they are 20 psi different relative to each other, they need to be less than 10 psi.
PLEASE leave a comment with your outboard motor's year, horsepower, and compression value. This way other people can get a feel for what they can expect.
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I have a 1994 Evinrude 50hp 35 at the Jet, My compression test showed 80PSI in both cyl and that was a cold test. Still have great power and starts nicely!
You might try squirting a little oil in cylinders and running compression test again! Rings and cylinders could be dry if it's been sitting a long time! Could bring pressure up a little! Thanks, Jim from Kansas!!
90 is good. My 25hp is at 90. I read 75 and above is optimal, but some said they will run at 60psi. As long as they are within 10% of each other.
I like to spray a little fogging oil in to act as lube between the piston cylinder and rings when checking compression
Great comment
Dont know if you'll still reply but I have a early 90s 25 hp murcury 2 stroke. Hasnt been started for like 20 - 25 years but it only has about 15 hours what should my first move on restoring in be. (Its been out of the rain this whole time)
What should compression numbers be for a 2000 evinrude 4 stroke 15hp please?
You put pressure on it kinda like if it was bolted down
I think you also hold the tube into the hole
I have a 1992 evinrude 25 and I got about 100 on each
Also remove both plugs and have the throttle in the wide open position while doing the test for more accurate readings
Hey, the motor will turn at more or less 350 rpm. The butterfly opening really has no bearing whatsoever !
hello, I have merc 25 1997 3 cylinder. I did the test on a cold and on everyone I have about 120psi. Is there more heat coming out? I can't find anywhere for this model how many should it be? Is this good, medium or poor? Regards!
These are good numbers
@@thisoldoutboard thank you for your answer :) should I remove the shift shaft from merc 25 by pulling it hard? is he somehow fixed there?
you must warm up engine before testing to get a corect reading on gauge,and fuel and oil will seal piston ring so compression will be higher
I would think the compression would increase after you crank it for a bit, or run it so that oil gets on the cylinder walls.
This is true
I have a 1985 Evinrude 25 hp. It cranks easy and runs on low throttle very well. Once I throttle it all the way down it tries to bog down. Any remedies or think you know what it could be?
Based on your description, this is pretty normal
have you ever found a solution to why? mine is doing the same
95 Johnson 25hp just checked the compression and I am reading around 75 on both cylinders is this ok?
If they're close and it starts relatively easily, just run it until it doesn't. Then you're looking at a rebuild. That is low though. I guess all depends on what you expect out of it.
Agree with hunterman600cc
Thanks for the info, thinking about trying to marvel mystery oil trick to see if I can raise it. The motor was sitting for a while so maybe the rings are stuck?
@@justinroberts9965 what is the marvel mystery trick to use?
John Creegan you can take the plugs out of the engine, pour a little mystery oil in the cylinders. Turn the flywheel a little with your hand just to get the oil moved around. Let it sit for about 2 to 3 days. Alot of times the oil will loosen/lubricate the rings up and make them seal a little better making the compression higher. Especially when you have a motor that has been sitting.
Ok. I bought what I think to be a 1957 johnson 35hp. It has 120psi on top cylinder, and 60psi on the bottom. What’s my next step?
If those are good readings you have a bad powerhead
Rebuild it!
I have a 73 85 hp mercury.
3 are good at 135 psi
1 is reading 102 psi.
Need rebuilding or use as is?
Base Line If it starts reasonably well if run it until I absolutely had to rebuild it
@@thisoldoutboard yeah start 2nd or 3rd try usually. Thanks for the reply.
You didn't crank the throttle handle open. It's suppose to be open for air to get in.
Compression is low because you tester hose is so long..it basically 2x the amount of space in the combustion chamber with all that hose. Get tester without the extension and retest. I'll bet it's much higher..