1972 Johnson 25 hp - 25EL72R

[aaronkcmo]

All,

I recently purchased an aluminum boat with a 1972 Johnson 25 hp motor - model# 25EL72R. I thought I was getting a good deal for several reasons, spending less than $500 for boat/motor/trailer.

The seller was a pawn shop and knew nothing about the motor, so I went into this project assuming that the motor had been sitting for quite a while. At first I bought a new gas tank, and fuel line. I attempted to start the motor and it started and ran for a few seconds. I did not want to run it longer because it was not hooked up to cooling water. I then took the boat to the boat ramp to try to take it for a test ride and the motor would not start. Long story short, the fuel pump had given out and that started a long list of repair and replacement of parts. To date I have rebuilt the fuel pump and carburetor; replaced fuel line/tank; replaced the plugs, plug wires, coils, points and condensers. Bad news, the motor still won't idle.

I rent a compression tester (like I should have done in the first place, I know) and the compression in both cylinders is 60psi. I squirt some oil into the cylinders and the compression goes up to 75psi. I am assuming now that it has bad rings.

After removing the cylinder head and the bypass cover I see that the rings are not fused to the piston and the cylinder walls show no sings of scoring. Also, the cylinder head and gasket look fine. My question now is should I break into this engine and replace the piston rings?

Taking the motor as 1/3 of the sale price of the boat and considering all of the ultra-cheap-sourced parts I've replaced, I currently have about $365 in the motor. I think that I could get away with just replacing the piston rings, head gasket, intake gasket, bypass gasket, top and bottom crank seal and the oil/vacuum lines spending only about $100 plus all of my time and labor.

It seems good to me because good used 25 hp motors are running in the $800-1000 range, which is out of my range. Are there any surprise costs I will definitely incur when breaking down this engine? Are there any other parts I should absolutely replace or just ones that show excess wear?

If it's not obvious; money, time and passion are three good things to have and 2 out of 3 ain't bad. Thank you for reading my post.

 

[JB]

Re: 1972 Johnson 25 hp - 25EL72R

Howdy Aaron.

Welcome to iboats.

Quit fixing what ain't broke. 60 psi is fine for a rope start outboard and most of the parts you replaced weren't broke, either.

Replacing parts is the most used, most expensive, least effective and least efficient troubleshooting method known to man.

Put her back together, get a factory Service Manual and do troubleshooting and a link 'n' synch by the manual.

 

[aaronkcmo]

Re: 1972 Johnson 25 hp - 25EL72R

I'm afraid all of those other parts were broke. Looking back the only think I really didn't need to do was rebuild the carburetor and replace the spark plugs, but what could that hurt. The fuel pump was bad, the coils, points and condensers were all bad and needed to be replaced for the motor to run at all.

From what I have been reading the compression should be around 100psi (granted I don't own an OEM repair manual).

This motor is electric start as well.

Also, I still have the idling problem even though the carburetor has been rebuilt (thoroughly) and the ignition tests fine.

 

[milliesdad]

Re: 1972 Johnson 25 hp - 25EL72R

First off, get the factory manual.

Second, take apart the carb, rebuild it, using new float and needle and seat valves and new gaskets. Remove the welch plugs and clean the innards of it, blow compressed air thru all passages.

I'm guessing the carb isn't right yet.

 

[aaronkcmo]

Re: 1972 Johnson 25 hp - 25EL72R

I see that I will need to purchase an OEM manual.

I wish it were as easy as rebuilding the carburetor. I've already done that very well. I've replaced the float, float valve and gaskets. I've removed the welch plugs and thorougly cleaned all passages before and after soaking the carb body pieces in carb cleaner overnight. The needle valve looks brand new and the needle seat is clean. The main jet was also very clean. Pretty much all of the passages are visible when the welch plugs are removed and the carburetor is squeaky clean. It was also very clean when I took it apart. It looked as if it had just been rebuilt, but I went ahead and did it anyway. The carb rebuild had zero effect on the engines performance. Currently the needle valve is set at two turns out, but I can't do anything else with it because the engine won't run at low speeds.

It's not that the engine just won't idle. It won't run at all unless the throttle is open to about 15% and it won't run under approximately 1000 rpm.

Forgive me for not writing the entire story, but when the ignition parts were slowly dying on me I was able to verify that the idle orifices of the carburetor were operating because I could observe liquid fuel being sucked straight through from the idle orifices to the exhaust when attempting to start the motor.

If the piston rings weren't a problem why would the compression shoot up 25% after squirting oil into the cylinder? I thought that was a tell-tale sign of bad rings.

 

[TN-25]

Re: 1972 Johnson 25 hp - 25EL72R

Welcome to i-Boats. I see that your motor is an electric start long shaft since the model is 25EL72R. It is also a 50th Anniversary Series. That motor is one of the better ones ever made by OMC. There never was any means of battery charging on those motors, so one of those solar-powered trickle chargers would be a great thing for out on the water.

I concur, invest in the proper OMC manual for your particular motor. Also don’t run that motor out of water as you can destroy an impeller within about 5 seconds by running it dry. Since the motor is new to you I would say that it is mandatory for you to replace the impeller anyway. On your motor it is relatively easy since you have an access cover to disconnect the shift rod to aid in the dropping of the gearcase. I will encourage you to look at the sticky post at the top of this forum entitled “Top Secret File" and look inside for "How to awaken a sleeping outboard”. It will cover all the things that should be done to ensure a good running and reliable outboard, or at least get you going until any other shortcomings are uncovered. That should be the first order of the day. You may find that after you get your motor running, your compression readings may improve as the rings get freed up.

Below is a picture of a short shaft 25 from the 1972 brochure.

 

[aaronkcmo]

Re: 1972 Johnson 25 hp - 25EL72R

Welcome to i-Boats. I see that your motor is an electric start long shaft since the model is 25EL72R. It is also a 50th Anniversary Series. That motor is one of the better ones ever made by OMC. There never was any means of battery charging on those motors, so one of those solar-powered trickle chargers would be a great thing for out on the water.

I concur, invest in the proper OMC manual for your particular motor. Also don?t run that motor out of water as you can destroy an impeller within about 5 seconds by running it dry. Since the motor is new to you I would say that it is mandatory for you to replace the impeller anyway. On your motor it is relatively easy since you have an access cover to disconnect the shift rod to aid in the dropping of the gearcase. I will direct you to look at the sticky post at the top of this forum entitled ?How to awaken a sleeping outboard?. It will cover all the things that should be done to ensure a good running and reliable outboard, or at least get you going until any other shortcomings are uncovered. That should be the first order of the day. You may find that after you get your motor running, your compression readings may improve as the rings get freed up.

Below is a picture of a short shaft 25 from the 1972 brochure.

Thanks for everybody's replies.

If I were ever able to take this boat out I would always bring the battery in the house when I park it. I built a nice custom battery/ignition box which I would not want to leave outside with the boat. I also have a Deltran battery tender which I am very happy with. I would love to have a solar powered charging system, but that sounds expensive.

That thread on 'How to awaken a sleeping outboard' was definitely a good resource. I found it early on and have followed it as much as possible.

I've also attempted to revive the piston rings using sea foam. I laid the motor down so the cylinders were facing up and filled each cylinder with the decarb chemical one at a time so that all of the chemical was forced through the ring grooves. After that I also ran a rich mix of sea foam in the fuel for an extended bucket test. This is where i'm at now. The sea foam had no affect on compression, it only made a lot of smoke, but frankly I wasn't very confident that a chemical was going to fix the problem especially when I could tell that the rings weren't seized.

I hadn't mentioned the lower unit yet because I haven't gotten that far. Thanks for the advise on the impeller. I already have a new one, I'm just waiting to get the powerhead running well before I put it in.

 

[aaronkcmo]

Re: 1972 Johnson 25 hp - 25EL72R

Allow me to reduce confusion by rephrasing my main question.

Let's assume for the moment that all other parts are good (carburetor, ignition), but the piston rings are bad. I have $365 into the motor now and I think I can put new rings in it for around $100.

If I parted the motor out I'm sure I could make back my investment, but I don't think I could make enough to buy another used 25hp motor in the $800-1000 price range.

Is it worth going in to replace the rings or will I definitely incur costs that would make the project prohibitive?