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Old 10-07-2008, 09:49 PM   #1 (permalink)
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Only 1 spark plug is black??...HELP

I have an interesting problem. I had a new motor done up after a lifter faliure. I have about 300 miles now in it and the #1 cylinder spark plug is black. Shiny and black not dry shooty or real oily.

All other plugs are a nice light tan. Any ideas what this could be?

I have checked compression and all cylinders are dead even. I checked any visible rotor and cap problems (both are new). I even switched out spark plugs with another cylinder.

There was one thing I was considering is that the Victor Jr. head was repaired by Fox Lake when someone went into the push rod hole while porting.

They put a brass sleeve in the pushrod hole and repaired the inside of the intake runner on the head with what looks like JB weld. When I bought the car it was like this and the old engine never had this problem.

If the reapir were to fail slightly would this be the problem I would see and what would be the bast way to check for this if it was not visible enbough to the eye.

Thanks for any help I can get. I am really lost.
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Old 10-07-2008, 11:26 PM   #2 (permalink)
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Re: Only 1 spark plug is black??...HELP

Oil fouling is the only thing I can think of. It sounds like what my spark plug looks like on my trail 70 bike. You can always probe the intake port of oil if there is a leak.
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Old 10-08-2008, 12:07 AM   #3 (permalink)
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Re: Only 1 spark plug is black??...HELP

Perform a leak down test on that and a few other cylinders and see how much is leaking by the rings or valves. You can have good compression and still leak past the rings. Does it smoke at all? Just on start up after sitting cold? bad valve guide? I doubt the pushrod hole repair is the prob. but you should be able to see a stain from the oil in the intake runner of the head if it is. Try and look down the intake. If you can't see you will need to take off the manifold, but again I don't think thats the prob. but sure could be. If the push rod hole is the problem and it's much of a hole you should be running lean in that cylinder. To check for sure back off the rockers on the cylinder and pressurize that intake port and listen/watch in that push rod hole.

Was there oil on the threads of the spark plug? In my experience a black shiny smooth hard surface on the plug is oil, black soot is fuel. If it was very rich they would all be black. Sounds like oil to me. Do a leak test and report back what you find.
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Old 10-08-2008, 03:57 PM   #4 (permalink)
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Re: Only 1 spark plug is black??...HELP

Could be sucking oil from the manifold due to a bad gasket seal there.

Could be carb dripping and running into that cylinder. I had the same problem but a different cyl and it was carb metering block.
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Old 10-08-2008, 08:13 PM   #5 (permalink)
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Re: Only 1 spark plug is black??...HELP

Thanks for the responses.

I did a compression check and it came out good about 185# same as the others.

I have not done a leakdown. I guess I need to buy the tool to do it. It will be my first attempt. I did have the engine builder do it (at least he said he did) about 3 months ago when it was in for a rear main seal and I brought up the plug deal and he said all was good. He did change the intake gaskets in case. but problem is still here and he was no help.

No smoke at all seen on startup or acceleration. The smoke would also be hard to see since the pipes are dumped under the car. yes there is a little oil on the threads.

I do have steam that come out of the breathers when idling. Saw this when I put k&N breathers on the car. Cant see any with the billet breathers I used to have. Not sure if this is related or not.

I am really intersted in the metering block theory though. I can tell you taht after a drive and the car is hot I can hear and see some fuel squirting out of the front squirter once in a while until it cools down. I thought this was normal. Would this be something to look at?

Thanks again for the help!!!
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Old 10-08-2008, 08:30 PM   #6 (permalink)
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Re: Only 1 spark plug is black??...HELP

I would try a different carb if possible -- preferably one that's 100% ok.

Otherwise, yes the dripping out the squirters is telling you something. Too much fuel level? Vapor pressure (shouldn't be a problem while running). Carb is not correctly assembled (check valve installed in squirter?)

I would take the carb off hot and look in the manifold after a good run. Is there liquid all around the carb baseplate and in the manifold? There should not be.
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1970 Cougar, 3660 lbs
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Best 1/4 mi: 11.24 @ 119 MPH Best 1/8 mi: 7.13 @ 96.32MPH
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Old 10-08-2008, 08:46 PM   #7 (permalink)
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Re: Only 1 spark plug is black??...HELP

Hi Allenman,

Unfortunately I do not have another carb to try. I never messed with the carb or any in general but I will check out what I need to. Where would this check valve be. The fuel level seems fine right at the bottom of the hole.

I will check on the fuel on the bottom of the manifold.

What would vapor pressure be? I though when the car would do this was becuse the heat went into the carb after shutdown and percolated the fuel out the squirter. If this is not normal I am glad I mentioned it.

This is a 950HP carb if this helps at all.

So maybe this is the problem (I hope) ?
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