Black Spark Plugs

M

Molska

Seaman Apprentice
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Jul 26, 2010
Messages
35
So my spark plugs have always been black. The top cylinder the plug gets wet more so than the bottom. I have a new fuel tank and hose and i mixed the gas pretty much perfect 50:1 maybe + a (ml) or 2.

i have a 25 hp 1980 evinrude

and this is what i have done to it in the last week or so:

carb kit
new tank/hose
new impeller
2 new coils
2 new spark plugs gaped an .04/1mm or just a little under

its been there for years and i think its time for a good fix
 
C

Craig-

Petty Officer 1st Class
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Jul 25, 2010
Messages
316
Re: Black Spark Plugs

Your main jet should be 49D not 59D.
Don't over oil the fuel, 55-60:1 might work better, watch the temp.
Make sure plug gap is correct, you could try a bit wider gap.
Do one step at a time, and observe change in plug reading.
 
M

Molska

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Messages
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Re: Black Spark Plugs

I'm sorry i'm not to sure what you mean by wrong main jet or how do i know what or where to look?
 
C

Craig-

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Messages
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Re: Black Spark Plugs

Molska said:
I'm sorry i'm not to sure what you mean by wrong main jet or how do i know what or where to look?
Click to expand...

Remove drain plug on carburetor bowl, strait in is main jet. A strait shafted screwdriver with flat blade that fits the slot well should remove it. Very small number on the brass main jet will tell size.
 
F

F_R

Supreme Mariner
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Messages
28,195
Re: Black Spark Plugs

???I don't get it---where does it say you have 59D jet? Anyhow, it is in the very bottom of the carburetor, behind the hex drain plug, and takes a special screwdriver to get it out. Once you get it out, it has the size stamped on it. Buy unless you have reason to think it is wrong, why look?

If your objective here is to keep the plugs from being black, you are wasting your time. Black is normal. "Reading" spark plug color went out the window when CD ignition came in. The CD ignition is able to fire through all that crud. That is its main reason for existance.
 
C

Craig-

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Re: Black Spark Plugs

Just pointed out correct size. 59D is used in 35hp and may be incorrectly installed in his 25hp, not that hard to check it. Stranger things have happened. I disagree about spark plug reading. Plug won't run black if it is running right, but many who premix use too much oil giving false plug reading.
 
M

Molska

Seaman Apprentice
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Messages
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Re: Black Spark Plugs

Oh okay so maybe i'll just leave everything the way it is then, i was just worried about the plugs being wet and maybe i'll do a 55:1 ratio instead i do, do a lot of trolling.

would it be a good idea to add one of those conditioners to the fuel like you do on your car?

But i guess i could check he type of jet that i have and change it if needed
 
Tim Frank

Tim Frank

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5,333
Re: Black Spark Plugs

I agree with FR....spark plug colour is more indicative (with CDI ignition) of manner of operation....lots of trolling etc.

Where did the 49D come from?

And .040 sounds like way too big a gap....where did you get that info and what plug are you using?
 
jasper60103

jasper60103

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Sep 18, 2008
Messages
2,055
Re: Black Spark Plugs

Tim Frank said:
...

And .040 sounds like way too big a gap....where did you get that info and what plug are you using?
Click to expand...

0.040 was the original spec stated in the OEM service manual. Champion has since changed it to 0.030.
 
Vic.S

Vic.S

Rear Admiral
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Messages
4,701
Re: Black Spark Plugs

Just to confirm that the current recommended plug gap is 0.030" (0.7-0.8 mm) but use that or 0.040" (1.0 mm) or anything in between ... whatever works best

The currently reommeded plugs are QL77JC4, or L78V surface gapped, or QL82C.

QL82C may be a little better than QL77JC4 if trolling a lot.

Check also the adjustment of the slow running mixture needle.

Screw in until it falters or shows signs of running weak and then back out until it just runs smoothly again. The full detailed instructions by Joe Reeves are on the Engine FAQs board at http://forums.iboats.com/showthread.php?t=167352
 
C

Craig-

Petty Officer 1st Class
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Jul 25, 2010
Messages
316
Re: Black Spark Plugs

Check the main if you want, if you are original owner chances are it is the correct jet size. New plugs gapped correctly and don't over oil the fuel. The wider gap won't hurt anything, but start with .030 gap and see if things improve. Sometime a wider gap will help if doing lots of slow trolling.
 
M

Molska

Seaman Apprentice
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Messages
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Re: Black Spark Plugs

Oh okay, ya .040 was in my owners manual and i've always been using Champion QL77JC4 i try to stay as original as possible. But i'll adjust the gap to 0.030 or so. i am also the original owner. i don't want to keep fooling with the carb i just rebuilt it and got the engine firing. The plugs and power pack were my next job.
 
F

F_R

Supreme Mariner
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Jul 7, 2006
Messages
28,195
Re: Black Spark Plugs

There is nothing wrong with the power pack if it is running on both cylinders.
 
F

F_R

Supreme Mariner
Joined
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Messages
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Re: Black Spark Plugs

Craig- said:
I disagree about spark plug reading. Plug won't run black if it is running right, but many who premix use too much oil giving false plug reading.
Click to expand...

Just for the heck of it I went out and pulled the plugs out of my own personal motor. This motor is 26 years old, and runs absolutely perfect. Nothing has ever been done to it other than change the impeller a couple of times just because.... And gear lube changes of course. And oh yes, I did change the plugs about 5 years ago because I was going to tow it 1500 miles up north on vacation. But the plugs didn't need to be changed, I just did it just because....

I will say that this motor is rarely ran at over 4000rpm. It tops out at 34 mph @ 6000rpm. (35hp)

Running L77JC4 at .040"

OK, OK, I will admit that I err on the side of too much oil. Simply because the tank won't hold a full 6 gallons + oil without being slop-over full. More like 5 1/2 gallons.
 

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M

mrcj001

Petty Officer 1st Class
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Messages
313
Re: Black Spark Plugs

One must remember, we are trying to burn gasoline mixed with oil. The oil is there to lubracate the cylinder walls and the gasoline is there to power the engine.

No dout, one will have unburnt oil on the plugs.

Thats why the CD ignition is used today.

Actually, if you dont have some black on the plugs, there could be something wrong with the fuel delivery or other things.
 
M

Molska

Seaman Apprentice
Joined
Jul 26, 2010
Messages
35
Re: Black Spark Plugs

Okay fair enough my plugs look pretty much the same and LOL for going and pulling your plugs hope it wasn't to much trouble LOL.

Thanks for all the suggestions i was just curious cause i had a mechanic rev the **** out of my engine and giving me heck that the oil gas ratio was wrong blah blah blah.

Now the only reason i was looking at the power pack was because my 25hp is running like this Johnson 50 at full throttle:

http://www.youtube.com/watch?v=DKbWcw2JRY8
 
O

OptsyEagle

Lieutenant
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Sep 13, 2006
Messages
1,356
Re: Black Spark Plugs

I agree with FR. I always have some wet blackish oil on my plugs, although not usually quite that much. One last thing you could look at perhaps would be your thermostat. If it has failed open your engine may be running cold a lot longer and not burning the fuel as well during that time. If the t-stat is difficult to look at then I might wait until I fouled a spark plug before I would go to too much trouble. Just keep it in mind.

My last piece of advice, always keep a spare set of plugs and a socket wrench in the boat just in case.
 
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