73’ 25hp Johnson smoking

[Rockyf]

I need some help/advice,

I recently purchased 14’ Starcraft w/25hp Johnson outboard. The boat was in a family friends backyard under cover for 10 years. The guy that owned it said he’d start it up every few months. He said he could never get his wife to go out so he got rid of it.

(This is my first boat not a mechanic but do what I can)
Heres the issues. It initially started up fine but seemed to run a little rough and smoked more than it should.
Motor 25R 73A this what I’ve done.
-replaced plugs JC4? Gap .032
-replaced both ignition coils
-replaced condensers
-replaced points and wick gap .02
there was a small amount of oil/gas? On top of the
armature plate.


when I start it up it still smokes more than I believe it should. Initially it runs a little rough. But after a few minutes runs much better. I can’t idle all the way down or it dies if I keep the idle up just a little maybe 10-20% throttle it runs fairly smooth. I have synthetic oil mix 50:1 with 2oz per gallon sea foam. I’ve run the motor on and off over the last several days. Maybe 30-45mins total. Their is a noticeable amount of oil/gas? In with the water barrel.

Could I have some bad seals? Or need to adjust/clean the carburetor? The motor itself looks pretty good visually for a 45year old motor.

What do I do next?

thanks for any help or advice
Rocky

 

[racerone]

Replace the water pump impeller.---Post compression test numbers first.

 

[Crosbyman]

oil/gas in the tub is very normal since a lot of gas/oil gets to exit the exhaust ports when the piston closes up

modern injection engines inject the fuel after the pistons close up


smoke… is probably more apparent if if you run it in a tub… on the lake it will dissipate faster and be less apparent to you

as suggested above replace the impeller do compression clean the carb (take it apart !!)

if that engine was properly oiled, stored properly you probably have a very good runner

 

[Tassie 1]

Just use it as is,
dosen't sound as if you have any major issues,

old outboards smoke a bit more than newer models,
Some oil in the tub is nothing to worry about,
they all do that...

just use the recommended oil/ fuel mix for that motor

 

[lindy46]

Seafoam in the gas will help clean carbon build-up in the cylinders, but will cause more smoke. After you've run it for awhile smoking should be less.

 

[flyingscott]

Are you ising fresh gas mixed at 50-1.

 

[Guest]

I have this exact motor, 73 Johnson 25. These are solid, fine running engines.

They smoke at first when they're cold, but after they warm up, the rings expand and they stop smoking.

Be sure you're mixing 50:1 fuel mixture (16 oz. of oil for 6 gallon tank of gas)

Running SEAFOAM in a tank is a good idea, that will clean the carb out.

I run 89 pump gas in mine, with a good quality outboard oil.

These engines don't like to sit , the more you run them, the better they run.

 

[racerone]

Captain E-----Are you sure that the smoking stops because the rings expand ?----Could you explain how this happens ?

 

[thatone123]

Some claim that some WWII era aircraft had pistons and rings designed so that the motors made a real racket like knocking noise when first started until they warmed up and the big jug pistons and rings expanded. I know the p-51 Mustang and others had a oiling system that you started 2 minutes before the engine was actually started so that the engine especially the valve train was well oiled. Imagine that. Many today cannot even wait 2 seconds in a car before they race off. Flying a B-17 took lots of mechanical knowledge as the engines had to be adjusted in every change of altitude, speed, rpm and etc; to get the most out of the motors.

 

[Guest]

There are a few things that can make a motor smoke when cold.

Heat expands the piston rings when the motor warms up and any blow-by of additional fuel/oil mixture slips past the cold rings in addition to the normal fuel charge. The motor is running "rich" and can smoke.

Another thing that can make a motor smoke is the inital mixture setting of the carburator, When the engine is hot, this is when you make you final low speed jet adjustments for idle and low speed running. (your engine has a "fixed" high speed jet)
While this may make you motor run great while its hot, when its cold, the adjustment me be set too rich until it warms up. Hence , you will get smoke.


Fuel can evaporate in the fuel bowl and leave an oil residue, when you squeeze the bulb to restart the engine after its been sitting, yhere is more oil in the fuel bowl than just your 50:1 mixture. When the engine fires off, you are burning not only your fresh fuel mixture, but also the leftover oil in the fuel bowl, which makes excess smoke, this eventually burns off and your engine stops smoking.

Most of these issues go away after about 10 minutes of initial running.

 

[racerone]

The " fuel / oil mixture slips past the cold rings "----So where does it go ?-----My opinion is that oil and lubrication in a 2 stroke is not well understood.

 

[oldboat1]

Seafoam is a mix of diesel fuel and proprietary solvents, I think. I always figure that putting any of the various solvents in the tank was more likely to loosen up and send contaminants from the tank to the carbs.

 

[Crosbyman]

read somewhere… 1/3 naphta 1/3 diesel fuel 1/3

methyl alcohol or iso ​

 

[oldboat1]

I've used kerosene and whatever solvents are available to clean out tanks, which isn't very elegant I guess. For cleaning carbs, the only thing that works for me is tearing them down and soaking. I have a Rochester quadrajet that needs cleaning this Spring, but will farm that out to the boat shop that stores the boat. Outboard carbs seem easy, with some exceptions. Inboards probably are too but I have a mindset about them -- like the little square OMC fuel pumps that frustrate me (big thumbs, poor eyesight).

 

[Scott Danforth]

-My opinion is that oil and lubrication in a 2 stroke is not well understood.

I agree.....I myself have a reasonable handle in it, however not to the point that some do.

 

[Rockyf]

Thanks for all the advice! I’m running 92 octane ethanol free gas in it. It seems the more I run it the better it does.

 

[Crosbyman]

oldboat1....

"like the little square OMC fuel pumps that frustrate me (big thumbs, poor eyesight)". ​

agree but I found that the frustration is mostly fitting the springs and mushrooms caps so what I do is glue the springs on their respective mounting nipples with a touch of crazy glue same for the mushrooms on top of the springs ... just a touch of glue and they will stand up on their own while layering the other parts

the glue prevents flying mushrooms to oblivion

As to the orientation of the layers I scribe the pump with a black ink pen BEFORE taking things apart … another way is to scribe the outside edges with an engraving tool for permanent markings .

another solution is to go Chinese ….

https://www.ebay.com/itm/1x-Fuel-Pu...774057?hash=item5d7ec4a129:g:NyoAAOSwQfRcU-O~