Problem with 1984 Johnson 25hp: plugs get dirty

[Pascastel]

Hi,

I have a small boat in Mexico, with a 25hp Johnson 1984. I just come back from a 3-4 weeks trip with it, fishing almost everyday strating from the shore.
The motor was running fine but things seem to get worse and worse: the plugs was getting dirty as well as the pistons and everyting inside the engine.

Use: The motor was used 90% of the time for trolling at 7-9 kmph.
Symptoms: with new plugs the motor start fine, but after few hours the plug get dirty, to the point that the motor have some misfiring (the accelaration is not fluid at all, it stops and restart accelerating) and its getting worse and worse. It only restart replacing the sparkplugs. Sometimes going faster for few minutes have made things better. The problem is that, we have been doing that during 3 weeks and I think the motor is dirty inside (when we srew off the dirty sparkplugs, the piston inside look dirty).
The motor have no termostat (they took it off), but the water is 83 degres Fahrenheit. The water out of the cooling pump looks 10-15 F degres hotter.
It is written on the motor 100:1 concerning the oil mix. We tried both 100:1 an 50:1. It just looks that the sparkplugs where getting dirty faster.
The only sparkplug available in Mexico were the champion L92YC and NGK B8HS10 and B7HS10
The champion were better, the motor was dirty after 20 hours running one time, and we retried them another time after trying the NGK at the end, it was dirty in few hours.
The NGK were much worse, everytime dirty quickly.

My opinion
The plugs aren't the good ones. I should bring the good plugs to Mexico (champion JC4) next time and cleen the motor with Seafoam.

My question
What do you think ? Can that be some other problems ? (thermostat?)

Thanks everyone

 

[nwcove]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

you need to stay with the plugs that were spec'd for that motor, and put the t-stat back in it. ( id also add some seafoam to the fuel to do a gentle de-carb)

 

[mekkamaz]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Ok. You have to put the thermostat back again...does not matter the temp. You are not running at a correct working temp, therefore you have an incomplete combustion...My boat is in Mexico also and do not have the problem, but my therms. are in place (V4) so I can say is not fuel related..Stick with the propper spark plugs.

 

[nwcove]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Ok. You have to put the thermostat back again...does not matter the temp. You are not running at a correct working temp, therefore you have an incomplete combustion...My boat is in Mexico also and do not have the problem, but my therms. are in place (V4) so I can say is not fuel related..Stick with the propper spark plugs.

......isnt that what i just said? lol

 

[Pascastel]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

The water is 83 degres. The cooling water is almost 100 degres. Is the cooling water is hotter than the initial water, I suppose that the motor is at least 110 120 degres. Is it enough for cold seizing ? Air the between 88 and 94 degres.
It is looking stange to me... any experience with cold seizing ?

Thanks

 

[nwcove]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

i think your motor should run at a water temp of around 140, air temp is irrevelent, even at 50:1 mix, you shouldnt fowl plugs on a regular basis. ( i have a1985 omc 4.5 hp, that is spec'd at 100:1, its been run 50:1 since new, and still has the original plugs.....the motor is used for low speed trolling 95% of the time) you need to replace the t stat , and see if it changes anything)

 

[jasper60103]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Good advice given. Just wondering why the Tstat was removed?

Oh, remove the 100:1 sticker from the motor. OMC change the requirement back to 50:1. My '88 Johnson 30hp had the same label.

 

[mekkamaz]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

......isnt that what i just said? lol

Maybe...but I think I was writing mine almost same time you post yours.....did not have the chance to read it!!

Anyhow, two agreeing something is better, right? Cheers!!

 

[Pascastel]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Good advice given. Just wondering why the Tstat was removed?

It was like this when I bought it. I don't even know where it should be placed and how I can put another one. It looks that removing the thermostat is pretty frequent around local fishermen.

 

[Pascastel]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Is it easy to put the entire thermostat system?

 

[F_R]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

That motor is supposed to have Champion L77JC4 plugs. I have the same motor, except mine is a 35hp. (25hp is just a de-tuned 35). It is run at slow idle to maybe 4000 rpm 95% of the time. Max full throttle RPM is 6000 if I open 'er up. The plugs in mine have been changed only once since new and they didn't really need it then. But if you were to take them out now, they would look like crap (see picture). Doesn't matter, they run just fine like that. That ignition system is able to fire right through the gook. I think I would be safe in saying this motor has never missed a beat since the day it was taken out of the box.

Um...you are running TC-W3 oil----aren't you? I hope not car oil and leaded gas.

 

[nwcove]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

should be just a new gasket and t-stat. basic maintenance.

 

[Pascastel]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Yeah.. another question: The termostat is cuting/opening the circuit which manage the cooling system. But will it only turn it on and off, or will it manage the amout of water entiring the cooling system ?
Why I ask that... When we use it, the motor is kept on during few (3-4) hours, the cooling pump would have started after few minute anyway. In a 4 hours fishing trip, the water pump runing from the begining... will it change something ? It is a mather of 4-5minutes in a 4 hour fishing trip...

 

[Pascastel]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Um...you are running TC-W3 oil----aren't you? I hope not car oil and leaded gas.

Yeah, TCW3 2 strokes marine motor from yamaha.

 

[AlTn]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

it controls the water exiting the block...the water pump is "working" anytime the driveshaft is turning...will it change something?..maybe, if there's a lot of salt or corrision buildup in the cooling system rendering it marginal, the thermostat can become just an added blockage and the motor may overheat

 

[kbait]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Install thermostat and correct plugs(.030"). Should run fine. Check head temp first at idle (after running several minutes) and after a wide open run. You should be able to touch the spark plug bases for a couple seconds before it's uncomfortably warm. If it's hot-hot, you have a restricted cooling flow. It'll likely be fine since it cooled w/o thermostat.

Plugs show their admiration to proper running temp (140 or whatever) by not fouling anywhere near as often.

De-carb for sure. Good luck!

 

[Pascastel]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

Hi, Thanks all for your reponses.
First, overheating is not a problem at all for my motor, the water flow well in the cooling curcuit. The water going out it 10-15 degres F hotter than the seawater.
Everyone agree that:
-it needs the good J4C plugs (J6C if I do a lot of trolling ?)
-It needs a thermostat
-it needs a decarb

I don't know how works a thermostat. Is it something only mecanical, like a small valve opening in the water circuit allowing the water to flow ? Or is it like an electrical sensor opening a circuit electricaly ?
I mean... do I just need a thermostat (and the rubber part that comes with it) or will I need to put some electric connection back ?

Thanks a lot everyone !

 

[Pascastel]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

I mean... is this thing connected to anything electricaly ?
http://www.ebay.com/itm/Thermostat-..._Accessories_Gear&vxp=mtr&hash=item4cfd77c7c5

 

[AlTn]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

no electrical connection to the thermostat

 

[nwcove]

Re: Problem with 1984 Johnson 25hp: plugs get dirty

not j4c or j46 plugs.....go with what was spec'd for your motor! the correct plug was mentioned above. ( using the wrong plugs may cure your overheating problem......but not in a good way! .....a motor that has holes in the pistons stays very cool)