low compression

[mikeaga]

I have a 1972 4 hp johnson sea horse. The compression is only 50 psi. should i even consider fixing it?

 

[tx1961whaler]

Re: low compression

Yes. 50 psi on a rope start could be OK. It's pretty hard to get a good reading using a pull rope.

 

[JB]

Re: low compression

Is that 50psi on each? Was the engine warmed up? If you did the test correctly (see Top Secret file) she should be okay.

 

[emoney]

Re: low compression

Just by guessing, as I've not done a compression test (maybe I should), but I'd bet my little Evinrude 2.5hp doesn't have more than 50lbs. Like 61whaler there said, might be a lot tougher to pull if got to be too high? Is the motor running poorly, btw? If so, what are the conditions (what's it doing)?

 

[kfa4303]

Re: low compression

+1. She'll probably run, believe it or not. You can try spraying a bit of WD-40, or Deep Creep into the cylinders to help free things up. The compression will probably also increase once the motor has had a chance to warm up after running for a bit. The compression seems ok. All the rest can be fixed with ease. Points & Condensers, Carb kits and coils are only about $20 each and you can get them right here at iboats.


http://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1972&hp=4&model=4206S

 

[Rick.]

Re: low compression

I guess there is lots of support above for it being a keeper engine. 50 is on the low side but like others I think it will come up once you get it running well. My own personal 71 - 4HP increased by at least 10% compression after I did a Seafoam treatment to it. Right away I would check for spark on each plug wire with a spark gap tester and if that proves to be good I would give it a new carb. kit and a very thorough carb. cleaning. If you don't get the spark to jump 1/4 inch with the tester you should pull the flywheel and check for cracked coils, properly gap (and clean) your points to .020 and let us know how it's going. Ask any questions you like and you will get lots of good information from this forum. Be sure to look at the Top Secret File at the beginning of this forum as there is lots of good information there. I would also suggest you get an OMC service manual for your specific year. Try Ebay for that. Best of luck. Rick.

 

[mikeaga]

Re: low compression

I had a mechanic look at it. It will run for a few seconds after much pulling. He put new points and condenser and cleaned the carb. No change.

 

[Rick.]

Re: low compression

One thing to check is your intake gaskets. I've had trouble with mine since I first got it. It would run for an hour sometimes more and sometimes less and then just stop. One pull and it was off and running again. This year it would stop and I had a terrible time getting it going again. Many pulls and the choke almost shut and it would run but had no power. I pulled the reed plate thinking it might be a bad reed and they were fine. When putting it back together I noticed oil right to the bottom of the reed plate gasket. Put a new set of intake gaskets in it and she is running perfectly. All day long she never stops or even sputters. It was loosing enough vacuum that it wasn't pulling enough fuel from the carb. I assume your slow speed needle is 1 1/2 turns out form gently seated and your high speed is 3/4 turns out? Rick.

 

[mikeaga]

Re: low compression

I got the motor back fromm the mechanic. he says compression should be at least 80 plus. He said it would probably run out of the water or with muffs. i got it home put it in a talk it would not start. I drained the water and it started and ran. Mechanic says motor is junk . Is he correct?

 

[emoney]

Re: low compression

You really need to share some more details. What do you mean you "drained the water and then it ran"? Sounds like your issue is carb/fuel related, just based on the limited information you've shared. When was the last time the carbs were cleaned at the least? Are you sure you've got good, clean fuel lines? How about posting some pictures of the carb, for example, and let's have a look at it. I don't believe in the word "junk" until everything has been confirmed. Lots of mechanics are quick to take knowledge they know about some engines and apply them to all engines. Doesn't make it right, but it is what it is. How comfortable are you tearing into it to see what's what?

 

[mikeaga]

Re: low compression

Sorry about the lack of information. I put the motor in a barrel of water and it would not start. I emptied the water out of the barrel and it started and ran for a bit. The mechanic just put a new carb kit on it this week. I have a new fuel line and fairly new tank. the old line was from a 1960 40hp johnson and it was dry rotted. I have taken car engines apart but never boat motors. But I am willing once I get a manual. Oh also it is a 1976 according to the serial number.

 

[JB]

Re: low compression

There is something wrong, Mike. IFF the carb cleaning was thorough and correct then look for leakage in the crankcase, seals or bypass covers. I don't think it is scavenging properly.

BTW, NEVER start a water cooled outboard out of the water. You probably need a new impeller by now.

That engine is worth fixing. It is of a series that were the best outboards ever made, by anyone.

 

[mikeaga]

Re: low compression

this was the only time i have ever started a motor out of the water. I only ran it for about 10 or fifteen seconds. how do I check for leaks. You're saying I should buy a manual? lol.

 

[kbait]

Re: low compression

If you have a bad head gasket leaking cooling water into the cylinder(s), it will start and run for just a couple seconds before water gets pumped up to the waterjacket, entering the cylinder(s) killing it. That may explain why yours would run w/o water pumping.. also could explain lower compression. I agree that it should run fine on 50psi, but not w/leaky head gasket. If you change it out, check for flatness of mating surfaces. I use a flat file to confirm.

 

[mikeaga]

Re: low compression

Would'nt I see water on the plugs? I tried loading pictures. I have not figured it out yet.

 

[nwcove]

Re: low compression

that pic loaded. you need to get back to the basics, 50psi compression ...motor should run. new carb kit....should run,.. if the carb was properly cleaned, float set . have you checked for good spark? and just curious about where you had the work done to the motor?...dealership, car guy, lawnmower guy etc?

 

[mikeaga]

Re: low compression

Work was done from a old johnson repairman who now works out of his house. He moved to Georgia from Florida. Spark is good he put new plugs wire condenser and points. One side around the head is corroded the other side is clean. I have more pics just couldn't get them to load. The previus owner swears it runs. I can only get the one pic to load. It saya the others are too big.