SOLVED '73 Johnson 25 eating spark plugs

[p10]

Hello!
I have a 1973 Johnson 25hp (25BR73A) that suddenly have begun consuming large amounts of spark plugs. When I install new spark plugs it runs just fine the first 3- 5 hours. Then I start to experience loss of power at full throttle. In the beginning it's almost not noticeable. The revs drop for a split second. These drops then come more and more often and lasts longer, but only at full throttle.

The next thing to happen is that the engine starts running on only one cylinder (the top one). This happens at random speeds. At the same time will not run at idle and is difficult to start. In the end it only runs on one cylinder and I have to have almost full throttle to start it up.

At this point the plugs are clogged down by some kind of residue, and cleaning the does not help. Replacing them however gives me 3- 5 hours of troule free running.

I tried cleaned the carb but that did not seem to be the problem. I have swapped coils, but the engine still ended up just running on the top cylinder. I have changed the head gasket, witch was in a bad state. At that point I really thought that the problem was solved, but I was wrong.

What else is there that I can test out?

 

[retiredfornow]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Sounds like it's carboned up. You mixing your gas and oil correctly? Is it oil injected? What kind of oil you use? Run some Sea Foam thru it.

 

[dew2]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

http://forums.iboats.com/showthread.php?p=2648076#post2648076
READ THIS

 

[p10]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Sounds like it's carboned up. You mixing your gas and oil correctly? Is it oil injected? What kind of oil you use? Run some Sea Foam thru it.

I use a NMMA TC-W3 type oil. The brand is called Biltema. It's a cheap brand here in Norway. I use a 50:1 mixture.

 

[tx1961whaler]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Decarb the motor using the link that dew2 provided.
The fuel-oil mix is 50:1, TC-W3 rated outboard oil. You might switch to a full synthetic 2 cycle oil.
Make sure that you are running with a properly operating thermostat. If you are running too cold, it will carbon up, the rings will stick and you're done....

 

[tx1961whaler]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Might be hard to get Sea Foam in Norway. Johnson makes an equivalent called Engine Tuner

 

[p10]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Make sure that you are running with a properly operating thermostat. If you are running too cold, it will carbon up, the rings will stick and you're done....

The thermostat is faulty. When I changed the head gasket I discovered that it is stuck in the open position. This would not have been a big issue earlier as I would run WOT all the way to the fishing ground, stop and fish, then run WOT back. The last 3 seasons I have been doing a lot more trolling... There might be a pattern emerging here... Will investigate further.

 

[wilde1j]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Cold running will quickly cause carbon deposit build up.

 

[Tim Frank]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

What plugs are you running?

 

[p10]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

What plugs are you running?

I have tested different plugs from Denson, NGK and Champions. Last pair was Champions J6C, recommended by my local Johnson dealer, since I do a lot of trolling.

 

[Tim Frank]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

What gap?

 

[p10]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Whatever gap they came with from the factory.

 

[Will Bark]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Uh No, gaps from factory may or may not be correct, plugs used for trolling are gapped wider than for regular use I think they are supposed to be at .40 which is wider. I'm away from my manuals now but I think that's correct. Good luck

 

[tx1961whaler]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

That would be 0.040", 1.02mm

 

[cajuncook1]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

The thermostat is faulty. When I changed the head gasket I discovered that it is stuck in the open position. This would not have been a big issue earlier as I would run WOT all the way to the fishing ground, stop and fish, then run WOT back. The last 3 seasons I have been doing a lot more trolling... There might be a pattern emerging here... Will investigate further.

You need to replace your thermostat. It keeps the engine warmer and allows for better combustion of fuel and oil. A thermostat that stays open will keep the engine cooler but excessive carbon and coke will build up. If you are trolling a lot it will speed up the processes.

You definitely need to decarb your motor with Seafoam or comparable product. You probably have loads of carbon built up already, so a decarb is a must do. Champion J6C is appropriate plug and your spark plug gap should be .030 inch with a gauge.

Your 2 cycle TWC-3 oil is fine as long it states it meets the TWC-3 standards.

Things to do

1. replace your thermostat
2. gap your J6C plugs to 0.030
3. decarb your motor with Seafoam or comparable product very well. If you can get hold of some Seafoam, put an ounce or two in each cylinder to start dissolving that thickened carbon and coke. It will smoke like house on fire at first.
4. Add an ounce or two of Seafoam or comparable product to each gallon of gas (petrol) as on going maintenance as cleaning measures forever and ever

You should be in business after the above, the guys here on the forum gave you excellent advice, now its up to you if you wish follow through.

Anyway, I wish you good luck and the best of fishing!!! Please have a Pint and chips for me!!

 

[p10]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

Thank you for all your replies.

Could anyone try to explain why the carbon deposits would cause this spark plug problem?

 

[fireman57]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

The spark can't jump through a bunch of junk. It's like putting a piece of paper between the contacts.

 

[nwcove]

Re: '73 Johnson 25 eating spark plugs

Re: '73 Johnson 25 eating spark plugs

carbon build up can cause serious probs....in a two stroke or a four stroke......ever been in a car, that knocks, pings.....and wont shut off for a few seconds after the key is turned off? normally thats caused by major carbon build up. ( if you already havent .....replace ALL fuel lines, your engine might be trying to burn decomposing rubber from the inside of the lines)

 

[p10]

Evinrude/Johnson Engine Tuner

Evinrude/Johnson Engine Tuner

I have obtained a can of Engine Tuner from my local dealer. The instructions on the can differs from the instructions for decarbin with SeaFoam linked to in the beginning of this thread.

Engine Tuner instructions state that you spray the entire content of the can into the carb. While the engine is running at fast idle. The engine should then soak for 3-16 hours before starting up and letting it run for at least 15 min on fast idle.

Does this sound about right?

 

[seahorse5]

Re: Evinrude/Johnson Engine Tuner

Re: Evinrude/Johnson Engine Tuner

That motor has the energy transfer (ET) ignition system in it, not a traditional magneto with separate systems for each cylinder. The one set of points act as a ground circuit for the other set as the engine rotates.

The driver coil under the flywheel was problematic back in its day and the newer ones are improved versions. The original sparkplut was the UJ4J that had an auxiliary gap inside of it. Regular J4 plugs would foul quickly. IF the ignition will not jump a 3/8" gap while pull starting, then the plugs will always foul.

Combine the weak ignition with a worn motor and a sloppy carburetor, and you have a handful of problems. A worn crankcase upper will also cause the magneto plate to wobble and that will affect the points and timing of the motor. Sometimes a motor with a worn plate can run better by closing the point gap to about .015-.018" because as it wobbles, the points will open wider. That is a trial and error procedure. There is also a worn crankcase fix kit listed in an old service bulletin somewhere, but it was very expensive for what it was.