[buster]

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?

[Slicktop]

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

[toobroketoretire]

Originally Posted by buster

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.

[fishslayer143@yahoo.com]

Originally Posted by buster

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 ?

[buster]

Originally Posted by toobroketoretire

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

Originally Posted by Slicktop

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.

Originally Posted by fishslayer143@yahoo.com

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.

[Slicktop]

"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.

[buster]

Originally Posted by Slicktop

"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.

[minkus316]

I had a similar issue with a manual choke cable coming loose thus running very rich (at full choke all the time).

[buster]

Originally Posted by minkus316

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!

[vettex2]

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