1995 25hp Johnson 2 stroke J25EEOA rough at idle and in gear

[monster1]

I had the new to me 14ft jon out for a test run. This motor planes the boat at 15mph and WOT at 24mph with all 365lbs of me on the rear bench seat. It runs really good cruising. Seems to run rough at idle and in gear at trolling speed. The fumes are rich and chokes me out. PO said he "cleaned" the carb and "went through" the motor. That's all the info I have from him.

I'm big on not fixing things that aren't broken, but I dont want to keep running this thing if it's out of tune. Certainly don't want to destroy the motor by not keeping it in top shape. I want to try to add some fuel treatment to the tank to gently clean the carb to see if that solves my idle problem before I attempt to take it apart to clean it. All advice is welcome.

Thanks

 

[Rand]

That is somewhat normal for a 2 stroke johnson trolling.
They usually smoke pretty good after 10min or so... due to incomplete combustion.
What spark plugs are in it?

 

[monster1]

That is somewhat normal for a 2 stroke johnson trolling.
They usually smoke pretty good after 10min or so... due to incomplete combustion.
What spark plugs are in it?

Not that I'm trolling for miles and miles. Just putting it in gear and going slow, the motor starts running rough right away. It smoke if it gets a hard start and I engage it to move spots. I'll find put what plugs are in it. I'm curious to see what they look like after the PO "went through the motor."

 

[mk378]

Dual carbs or single? If the idle jet is clogged in one carb it will of course run on one cylinder at idle.

And as mentioned this is why trolling motors are a thing.

 

[JTK]

Is the fuel for sure fresh and the pre-mix correct?

If this engine starts easily, idles OK, has good throttle response and wide open throttle, this is a tougher troubleshoot, but I'd look into the carb(s) as @mk378 suggested.

 

[Tman220]

What's your basis for comparison? How much experience do you have with relatively large two stroke twin cylinder outboards? Any twin cylinder two stroke outboard will certainly vibrate a good bit at slow idle and loaded in gear.

Also these engines create a lot of steam from the upper exhaust ports which might appear to be smoke and running rich. What do the plugs look like? How about a video of it idling in gear?

Is this engine electric start? It's fairly common for the fuel enrichment solenoid to start leaking especially on an engine approaching 30 years old. There should be a solenoid with a red lever on the left side of the carburetor. If this engine is electric start you will have a primer that you hold down for fuel enrichment. If it's a key start you activate by pushing in the key. If it's a tiller than there will be a button you hold down while starting. Anyway this red lever is for manual enrichment if the battery is dead and they can sometime leak which would introduce more fuel at idle and cause it to run rich. Would not be as noticeable while under power.

 

[monster1]

What's your basis for comparison? How much experience do you have with relatively large two stroke twin cylinder outboards? Any twin cylinder two stroke outboard will certainly vibrate a good bit at slow idle and loaded in gear.

Also these engines create a lot of steam from the upper exhaust ports which might appear to be smoke and running rich. What do the plugs look like? How about a video of it idling in gear?

Is this engine electric start? It's fairly common for the fuel enrichment solenoid to start leaking especially on an engine approaching 30 years old. There should be a solenoid with a red lever on the left side of the carburetor. If this engine is electric start you will have a primer that you hold down for fuel enrichment. If it's a key start you activate by pushing in the key. If it's a tiller than there will be a button you hold down while starting. Anyway this red lever is for manual enrichment if the battery is dead and they can sometime leak which would introduce more fuel at idle and cause it to run rich. Would not be as noticeable while under power.

It's quite possible I just don't have a base to compare what this motor is doing. I've only owned 4 strokes and inboard engines. Here's a link to the video I posted to YouTube of the motor running.

 

[Tman220]

Looks to me like you have a good running old OMC. Looks absolutely normal to me. I have a lot of experience with a 1996 evinrude 28 hp spl which is basically the same outboard with maybe a different carb or intake manifold. They used that size engine from 20 hp all the way to 35 hp with changes to mostly the intake manifold and carb.

Also, keep an eye on the starter bolts, I had one come loose on the 28 hp and broke one of the studs off in the block. Nobody has time to to drill/extract a stainless stud/bolt from an aluminum block.

These outboards were designed basically in the 60's, they run great and last a long time but certainly are not known for their refinement and they are quite loud if you ask me. We nicknamed the 28 hp the grinder for a reason.

 

[Elkins45]

It's quite possible I just don't have a base to compare what this motor is doing. I've only owned 4 strokes and inboard engines. Here's a link to the video I posted to YouTube of the motor running.

That’s normal.

 

[97prizm]

I had the new to me 14ft jon out for a test run. This motor planes the boat at 15mph and WOT at 24mph with all 365lbs of me on the rear bench seat. It runs really good cruising. Seems to run rough at idle and in gear at trolling speed. The fumes are rich and chokes me out. PO said he "cleaned" the carb and "went through" the motor. That's all the info I have from him.

I'm big on not fixing things that aren't broken, but I dont want to keep running this thing if it's out of tune. Certainly don't want to destroy the motor by not keeping it in top shape. I want to try to add some fuel treatment to the tank to gently clean the carb to see if that solves my idle problem before I attempt to take it apart to clean it. All advice is welcome.

Thanks

On a boat forum someone posted a similar issue. They also posted that their Johnson wasn't the salt water version not sure the difference. One thing I noticed was
"
95% of the time what you are seeing is going to be carb related.

If you do end up taking them off, remember you need to take the plates off too and if your has idle jets, count the turns. These turn out 6-7 turns not 1- 1 1/2 like the other engines."
Hope this helps.

 

[monster1]

Thanks for the replies everyone. Guess the good news is that I don't have to rebuild a carburetor. Bad news is I might be looking into a four stroke in the near future.

 

[GooseGestapo]

Carburetor kits aren’t expensive. Nor are the carburetors very complicated.

I would suggest you might have put too much oil or, substandard oil.
I would only use OMC or Mercury branded 2-stroke oil.
16oz to 6gallons (50:1 ratio).
I ran numerous 2-strokes in my career. Burned up several motors in the early-mid ‘80’s running agency provided Oil Co. branded sub standard 2-stroke oil. It will carbon up the pistons and rings.
We mostly ran Mercs. The one Johnson 25hp we had we called “chugger” for the same reason. It was a good engine though.
I can recommend the 20hp Suzuki! I got one with a tiller and no electric start. It’s electronic fuel injected using the rectifier to create electric charge. The first pull charges the system, second pull fires on the first compression stroke!
Best small outboard I’ve ever run. 2mph faster than the 18hp Merc 2-stroke it replaced. (14’x48” PolarCraft modified V hull Jon, 27mph per GPS). Just sips fuel…
My only complaint is that I got into a shallow sand bar and loaded up the water pump damaging the impeller. I had to make a 100mi trek twice to the nearest Suzuki dealer to have it repaired (under warranty). They charged me $400 to replace the impeller and housing, and connecting a computer to the engine to reset the limp mode activated when it overheated. A $2400 portable outboard motor has a computer, throttle position sensor, air temp sensor, rpm limiter! It amazes me how much they changed in the 20yrs since I retired…
I had just replaced the water pump impeller, ignition trigger, and o/h the carburetor on my ‘84 Merc 18hp I’d owned for 29yrs. Sold it for what I bought it for… but it was taking a carburetor kit after every time I used it. (The legacy neoprene components don’t tolerate the current 2-stroke oils or unleaded fuel - even the no ethanol premium which is all I use except in automobiles).
But it still ran good… but could be difficult to start.
Now it’s out of warranty. Next impeller I’ll do. A computer wiring harness and disc is about $70 on eBay… Sayanara! Sports Center…!

 

[Donald]

Start with the easy stuff. New spark plugs and fresh gas with the proper oil mixture.

 

[97prizm]

I had the new to me 14ft jon out for a test run. This motor planes the boat at 15mph and WOT at 24mph with all 365lbs of me on the rear bench seat. It runs really good cruising. Seems to run rough at idle and in gear at trolling speed. The fumes are rich and chokes me out. PO said he "cleaned" the carb and "went through" the motor. That's all the info I have from him.

I'm big on not fixing things that aren't broken, but I dont want to keep running this thing if it's out of tune. Certainly don't want to destroy the motor by not keeping it in top shape. I want to try to add some fuel treatment to the tank to gently clean the carb to see if that solves my idle problem before I attempt to take it apart to clean it. All advice is welcome.

Thanks

A while back someone mentioned a spark arrestor as a culprit on their two stroke engine. Not sure about outboard motors.