black, oily spark plugs

B

bookryan

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Oct 17, 2007

Messages

5

• Oct 17, 2007

• #1

I pulled the plugs on my '71 Merc 650 and the ends are all black and oily. Is that right?

 

C

CharlieB

Vice Admiral

Joined

Apr 10, 2007

Messages

5,617

• Oct 17, 2007

• #2

Re: black, oily spark plugs

Time for a new set.

If they are not too old then it is also time to clean the carbs

 

B

bookryan

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• Oct 18, 2007

• #3

Re: black, oily spark plugs

Thanks for your response.
The plugs aren't charred black or anything. They're just covered with a thin, wet, black, oily residue that easily wipes off. Still think its just bad plugs?

 

C

Chris1956

Supreme Mariner

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Mar 25, 2004

Messages

27,148

• Oct 18, 2007

• #4

Re: black, oily spark plugs

Ryan, Those plugs could be normal. The gapless plugs last a long time. As long as they fire consistantly, I would leave them alone.

 

Texasmark

Supreme Mariner

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Dec 20, 2005

Messages

14,558

• Oct 18, 2007

• #5

Re: black, oily spark plugs

Surface gap plugs develop track marks the first time out (BTDT).....one reason I don't like them, but I ran a set in a '89 115 tower of power for 7 years with no problems.....course with 6 cyl I could have lost one and would not have known it.....possibly.....but the WOT on that rig was 6k and if one were loafing I'd know it.

Think about this: How do you shut down the engine? You switch off the ignition. Does the engine stop immediately? No! It takes a few revs for it to stop turning over. Well, the fuel/air system is still active and with no spark, guess what? The plugs are always wet and oily when you inspect them, unless you pull them immediately after a high speed run and the heat of the plug evaporates most of the moisture off them by the time you can get them out.

My 2c,

Mark

 

B

bookryan

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• Oct 18, 2007

• #6

Re: black, oily spark plugs

Thanks, all, for your advice.

 

M

MercFan

Petty Officer 1st Class

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Dec 31, 2005

Messages

347

• Oct 18, 2007

• #7

Re: black, oily spark plugs

bookryan, your driving style and application has a lot to do with it. Do you putter along most of the time, or WOT? Do you run for extended peroids or do you shut down and start up often? I spend most of my time on plane between 60-100% throttle, and I only start-up/shut-down 4-5 times in a whole day. I also run a decent grade of 2 stroke (not full synthetic though), with TCW3 rating. I know from the couple of 2 stroke motor cycles that I've owned that the really cheap 2 stroke oils leave more deposists than the better brands/ratings.

But since you can just wipe them off, and you have no performance, rough running, stumbling complaints, you're fine.

 

j_martin

Admiral

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Sep 22, 2006

Messages

7,474

• Oct 19, 2007

• #8

Re: black, oily spark plugs

I'd be concerned if I pulled my plugs and there wasn't a little oil on them.

John

 

G

gidds

Seaman Apprentice

Joined

Jul 14, 2007

Messages

48

• Oct 19, 2007

• #9

Re: black, oily spark plugs

Bookryan....

Not to hijack but...

I took this picture last night. Cyl 2 and 4 had oil on them. The others were mixes condition.....sorry for the bad pic but do these tell you anything about my condition........checked compression and got 115,125,125,117,125,120....

Thanks

 

j_martin

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Sep 22, 2006

Messages

7,474

• Oct 19, 2007

• #10

Re: black, oily spark plugs

1 and 6 are dangerously lean, 2 and 4 are rich. It's carb time for sure.

hope it helps
John

 

G

gidds

Seaman Apprentice

Joined

Jul 14, 2007

Messages

48

• Oct 19, 2007

• #11

Re: black, oily spark plugs

j_martin said:

1 and 6 are dangerously lean, 2 and 4 are rich. It's carb time for sure.

hope it helps
John

Click to expand...

John.....

do you mean rebuild, cleaning, adjusting or all????? Also, is 3 and 5 the way they are supposed to look?

Thanks

 

M

MercFan

Petty Officer 1st Class

Joined

Dec 31, 2005

Messages

347

• Oct 19, 2007

• #12

Re: black, oily spark plugs

Does 6 even fire ever? -> Check with timing light.
Check compression on all 6 cylinders.
I'd do all the suggested. Rebuild, clean, adjust from scratch (link&sync check faq section)

 

Texasmark

Supreme Mariner

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Dec 20, 2005

Messages

14,558

• Oct 20, 2007

• #13

Re: black, oily spark plugs

Yes on 3 and 5.

Mark

 

C

Chris1956

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Mar 25, 2004

Messages

27,148

• Oct 21, 2007

• #14

Re: black, oily spark plugs

Gidds, Is that an inline six or V6 motor? If it's an inline, #6 looks like water injestion, and the rest don't look too good either. On an inline, cylinders 2,4,6 should run a bit richer than 1,3,5 but yours show a lot of difference. I would cleanup the carbs and make sure the floats are set correctly. Maybe they are flooding a bit.

 

Texasmark

Supreme Mariner

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Messages

14,558

• Oct 21, 2007

• #15

Re: black, oily spark plugs

71 Merc 650 translates to I6 "tower of power".