Blackened spark plugs --> Fuel too rich?

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bluesmoker

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Hey I am new to outboards but relatively handy. I bought a used 15hp Evinrude (1990). I pulled the spark plugs recently and they look pretty blackened. I compared them with some web images that would say my fuel is too rich. Is there a simple fix to this? I run 50:1 so perhaps I could dial that back a bit, though from reading this forum 50:1 seems like the agreed upon standard. Is there a way a to nudge the motor a bit so it could run faster/hotter? Finally my motor has a knob right in between the rope starter and the choke that has been described to me as a 'fuel enrichment' knob. I was told to leave that at 6 o'clock and that it really only changes things at ide. Would that help?

Thanks for any help!
 
iwombat

iwombat

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Re: Blackened spark plugs --> Fuel too rich?

Your enrichment knob is for idle mixture. Your main jets are fixed and not adjustable. If your plugs are black it may be that you're running too cool - thermostat stuck open.

First thing you should do with a new-to-you used outboard is service the impeller and t-stat anyway, so now you have yet another reason to do that.
 
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bluesmoker

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Re: Blackened spark plugs --> Fuel too rich?

iwombat said:
Your enrichment knob is for idle mixture. Your main jets are fixed and not adjustable. If your plugs are black it may be that you're running too cool - thermostat stuck open.

First thing you should do with a new-to-you used outboard is service the impeller and t-stat anyway, so now you have yet another reason to do that.
Click to expand...

Are these two things that I can do myself or should I pay to have it done?
 
nwcove

nwcove

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Re: Blackened spark plugs --> Fuel too rich?

if you are comfortable with a wrench, dyi. just take a few pics as you go along, do some research and dont re-use any gaskets . i wouldnt even worry bout the plugs being black, its alot better to run rich than to run lean. (plugs are cheaper than pistons). and dont start mixing at 60:1 ! i mix my 50:1 motor to spec (25 liters of fuel/ 500 ml oil) and then add about 50ml more oil...just to be safe.
 
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dazk14

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Re: Blackened spark plugs --> Fuel too rich?

Are you using the correct spark plugs? Post what's in there.

How does it idle?

If it's loading up at idle(too rich), the plugs may not clean up during cruising.

Rotating the mixture knob clockwise will lean the mixture and lighten the color of the plugs.

You can rotate the knob up to 11 o'clock(the limit without pulling and resetting knob) without harm to the motor. RPM's dropping and/or a misfire will indicate you've gone too lean (which is part of the tuning process).

Just rotate knob counter-clockwise to clear up a lean condition.

Since you know the original setting is at 6 o'clock, you can always reset it.

Look to ebay for a factory(not seloc) 1990 9.9 Johnson or Evinrude service manual(it's blue). Ebay search 1990 9.9 Evinrude service manual. Looks like $35 delivered.

Waterpumps and thermostats(esp 1990) are a DIY job. The thermostats are a bit pricey, so test it. The waterpump kits are very reasonable, so plan to replace it if you pull it apart.

Lots of experts on that motor @iboats.

Good luck.
 
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bluesmoker

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Re: Blackened spark plugs --> Fuel too rich?

dazk14 said:
Are you using the correct spark plugs? Post what's in there.

How does it idle?
Click to expand...

I was using L77JC4 plugs but when I went to the shop they said the replacement plug is QL77JC4 so that is what I have in there now.

The idle is smooth but dies at the lowest throttle point.
 
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