1977 Evinrude 55HP -> Bad compression on one cylinder

I just bought this engine, and got it cheap because it idles badly. A compression test gave 130 psi on top, and 150 on the bottom.

He said he had been using it for slow speed fishing. :facepalm:

I hope the rings are carbed up on the top cylinder, is there some easy solution to this?

Re: 1977 Evinrude 55HP -> Bad compression on one cylinder

Run some seafoam through it
Clean the carburettors too

Re: 1977 Evinrude 55HP -> Bad compression on one cylinder

Before you spend any money on the carbs, look into the compression prob. Pull the cyl head and have a look at the gasket and the cyl's. 20psi is to much difference.

Re: 1977 Evinrude 55HP -> Bad compression on one cylinder

Before you spend any money on the carbs, look into the compression prob. Pull the cyl head and have a look at the gasket and the cyl's

Click to expand...

Yeah? 13 % difference, is it really that crucial?

I am a bit reluctant to do that now, since I fear ending up breaking one of the bolts. It is spring in Norway now, and I dont want to end up waiting for parts when summer is here. But on the other hand, I would like to replace the thermostat. Hmm.

It got the engine up running today btw. It seems to lack some tune up in general. Next thing now is to check the gearcase oil for water and renew, boil the carbs in citric acid and get the ignition timing adjusted.

If there are no big surprises tomorrow with the gearcase oil, I guess I?ll just order some seafoam and hope for the best regarding the compression difference. At least for this summer. After all, its just an old outboard...

Re: 1977 Evinrude 55HP -> Bad compression on one cylinder

I doubt that compression difference is your problem, Hans. Johnson actually called for 15% as maximum difference. Forget the surgery and do some troubleshooting of your idling problem.

Run a decarb on her, do a link 'n' synch and do a new compression test this way: http://forums.iboats.com/johnson-ev...ion-test-jb-313963.html?highlight=compression.

Let us know the outcome.

Re: 1977 Evinrude 55HP -> Bad compression on one cylinder

If you have poor compression the mtr will never idle right.

Re: 1977 Evinrude 55HP -> Bad compression on one cylinder

I would agree if the compression were poor. It isn't, it is within spec.

The Johnson manual says not more than +/- 15%. 130 and 150 is +/- 14.2%. In fact I believe those numbers are exaggerated by unusual procedure. I would expect a normal test would produce numbers like 108 and 120psi.

I am a fanatic about avoiding surgery until non-invasive procedures have been exhausted. Decarb and link 'n' synch don't use up bucks or risk breaking anything. I think a proper decarb will bring the correctly measured PSI closer and if the link 'n' synch are done correctly (with the leg in the water and in gear) the idle problem will go away. Worst case, there may be a carb cleaning problem.

Re: 1977 Evinrude 55HP -> Bad compression on one cylinder

The OMC manual I have says no more than 15 PSI.