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Discussion Starter · #1 ·
I had a miss that got progressively worse and I tracked it down to a fouled plug. I had recently checked and cleaned all the plugs so am surprised by this as I haven't had any tuning issues for a long while. Should I be looking for a bigger problem?
 

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I woud just replace the plug and see if it repeats. Plugs do go bad do to cracks in the insulator, deposits shorting it out, etc. If the new plug fouls out in short order then you might have a bigger problem. This assumes that your points are set right, wires are good and the cylinder has good compression.....etc. Here is an excellent article about plugs, it covers everything:

http://www.aa1car.com/library/sprkplg2.htm
 

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I had a miss that got progressively worse and I tracked it down to a fouled plug. I had recently checked and cleaned all the plugs so am surprised by this as I haven't had any tuning issues for a long while. Should I be looking for a bigger problem?

Over time the gap widens but otherwise don't "go bad". Was the fouling dark like burned oil? If so you may have a problem with the oil rings in that cylinder. Do you remember which cylinder it came out of? If it was #7 it could have fouled from fuel when pumping the throttle as fuel will run directly into #7.
 

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I had a miss that got progressively worse and I tracked it down to a fouled plug. I had recently checked and cleaned all the plugs so am surprised by this as I haven't had any tuning issues for a long while. Should I be looking for a bigger problem?
exactly what was it fouled with, Buster? wet gas, sooty dry carbon or greasey black oil ?
 

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Discussion Starter · #5 ·
Over time the gap widens but otherwise don't "go bad". Was the fouling dark like burned oil? If so you may have a problem with the oil rings in that cylinder. Do you remember which cylinder it came out of? If it was #7 it could have fouled from fuel when pumping the throttle as fuel will run directly into #7.
It is number 5

I woud just replace the plug and see if it repeats. Plugs do go bad do to cracks in the insulator, deposits shorting it out, etc. If the new plug fouls out in short order then you might have a bigger problem. This assumes that your points are set right, wires are good and the cylinder has good compression.....etc. Here is an excellent article about plugs, it covers everything:

http://www.aa1car.com/library/sprkplg2.htm
Thanks for the article, it is very informative. No points, I have a Pertronix.

exactly what was it fouled with, Buster? wet gas, sooty dry carbon or greasey black oil ?
I guess I could have supplied more info! It is a sooty black, dry, with only a very slight smell of gas.

I recently had all plugs out, cleaned them and put them back in.

I will do a compression test on this cylinder. BTW, no smoke at all out of the exhaust. I will keep you all posted, thanks.
 

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"I guess I could have supplied more info! It is a sooty black, dry, with only a very slight smell of gas.
I recently had all plugs out, cleaned them and put them back in. "

Incomplete combustion caused by rich mixture or weak spark is probably the cause. Could be low compression also, etc. Again, I would just replace the plug with a new one first and see what happens. It is an old plug that you cleaned and regapped and it could have gone bad. Just cleaning it can cause damage to the ceramics such as cracking or scratches which the spark can follow and arc to ground.
 

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Discussion Starter · #7 ·
"I guess I could have supplied more info! It is a sooty black, dry, with only a very slight smell of gas.
I recently had all plugs out, cleaned them and put them back in. "

Incomplete combustion caused by rich mixture or weak spark is probably the cause. Could be low compression also, etc. Again, I would just replace the plug with a new one first and see what happens. It is an old plug that you cleaned and regapped and it could have gone bad. Just cleaning it can cause damage to the ceramics such as cracking or scratches which the spark can follow and arc to ground.
I replaced it with a used plug that I had and test drove it a coupla miles. It runs great so am going to get a new plug for that hole, check compression and go from there. I recently had the carb off and now have readjusted it. Maybe that contributed to the plug going bad, will advise.
 

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Discussion Starter · #9 ·
I had a similar issue with a manual choke cable coming loose thus running very rich (at full choke all the time).
Thanks, choke cable and application are normal. Good news, I ran a comp test on that cylinder and it is at 155 lbs! I did it twice to be sure. Hoping it was a bad plug.

Toobroke, you mentioned apossible fuel issue with #7 cyl but this #5, any more thoughts as I DID do some minor carb adjusts to air/fuel mix?

BTW, I have 70 primary jets and one carb expert suggested I go to 72's, any comment? Compression est at 10.1:1, comp cam thumper, 750 Holley, Edelbrock RPM heads and intake. Engine is balanced and blueprinted and heads have been portrd and polished. Computer program by builder est. 440 HP? Info just to help with jet question. I have the jets and have changed out jets previously, just havent tried that large a size.

Thanks again guys, you are the best!
 

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Yes they can wear out. This is a used plug from a funny car. notice the melted electrode.

:2ni19wj:
 

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Buster, a larger jet will run richer.. if you are carbon fouling plugs already, I would advise against it..how much manifold vacuum do you have at idle.. your power valve maybe to high and opening when not needed ..PV should be 1/2 of idle vacuum...example..11 inch hg /5.5 power valve .....very easy to replace.
 

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i recently replaced the plugs on my wifes explorer (due to it missing) with i think champions. started it and it ran worse than before. tracked it down to two plugs not firing. cleaned the old ones, put em back in and it ran great. these were the bargain plugs at autozone. kind of a get what you pay for situation.. ill definitely spend the extra scratch next time for decent plugs.
 

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Discussion Starter · #16 ·
Buster, a larger jet will run richer.. if you are carbon fouling plugs already, I would advise against it..how much manifold vacuum do you have at idle.. your power valve maybe to high and opening when not needed ..PV should be 1/2 of idle vacuum...example..11 inch hg /5.5 power valve .....very easy to replace.

I have about 10 hg at idle. already put a 4.5 power valve in after discussion with holley. Since it is just the one plug, I wonder if. the problem is fuel related or no...
 

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I have about 10 hg at idle. already put a 4.5 power valve in after discussion with holley. Since it is just the one plug, I wonder if. the problem is fuel related or no...

No, even though the fuel doesn't get distributed 100% evenly it wouldn't make just one cylinder that rich. I would suspect a possible bad plug wire or carbon tracking in or on the cap. Is that wire routed far away from your hedders? At idle it may fire just fine but under a load the spark may be jumping to ground and the hedders would be the most likely place.
 

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Discussion Starter · #18 ·
No, even though the fuel doesn't get distributed 100% evenly it wouldn't make just one cylinder that rich. I would suspect a possible bad plug wire or carbon tracking in or on the cap. Is that wire routed far away from your hedders? At idle it may fire just fine but under a load the spark may be jumping to ground and the hedders would be the most likely place.
I found and cleaned some buildup on the cap and rotor contact points. Now I am looking at replacing them. Should I use aluminum or brass contact material? Mallory makes a cap that is more expensive than ac delco, could it actually be $10 better?
 

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I found and cleaned some buildup on the cap and rotor contact points. Now I am looking at replacing them. Should I use aluminum or brass contact material? Mallory makes a cap that is more expensive than ac delco, could it actually be $10 better?

The standard aluminum terminals are just fine as the secondary voltage is so high. Brass is better but not enough better to make any difference.
 
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