# Fouled Spark Plugs



## Dual Tempests (Mar 4, 2010)

Hello, I have a 1964 Tempest with a 1969 428, #16 heads, and a pretty big cam (so much so that I need a vacuum pump to run the brakes). Over the last year, I have been going through a set of spark plugs every 4 hours of so of driving (it is a weekend car). It turns them all black and the car backfires and pings terrible. Can hardely get it running. No plug is worse than any other. 

I finally tested the ignition and and compression and found the following:

Cylinder 1 - 189 PSI Wire had 143 Ohms
Cylinder 2 - 185 PSI Wire had 170 Ohms
Cylinder 3 - 184 PSI Wire had 133 Ohms
Cylinder 4 - 176 PSI Wire had 120 Ohms
Cylinder 5 - 191 PSI Wire had 108 Ohms
Cylinder 6 - 170 PSI Wire had 90 Ohms
Cylinder 7 - 178 PSI Wire had 83 Ohms
Cylinder 8 - 190 PSI Wire had 87 Ohms

Also, the coil read 4.3K Ohms between the center and either lead. 

Am I wrong in thinking that the compression is good enough and that a new coil and wires will solve my problems?

Many thanks,

Joe


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## likethat (Oct 5, 2007)

2 things can be happening the plugs could be to cold and the carb could be to rich or both. What does each plug look like. I would think the higher ohm wires would have worse fouled plugs


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## 1970 Lemans (Jul 25, 2009)

According to 1970 shop manual, resistance of secondary or high tension cables (ie, coil to distributor and distributor to plugs) should be in the range of 3,000 -20,000 ohms, so you definately do not have too much resistance. I would be inclined to say that is not the source of the problem.

In regards to plug fouling, according to manual, if the deposits on the plug is soft, fluffy, dry carbon then this usually indicates a rich fuel mixture, excessive idling improper operation of automatic choke or faulty carburetor. If the deposit is hard baked-on, black carbon, the result is indicative of use of too cold a plug. If wet, black deposits are indicated, this usually suggests worn piston rings, pistons, cylinders or valve guides.

What type of deposit is it?

Compression seems reasonable to me.


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## jetstang (Nov 5, 2008)

It's rich, lean it out, or run it harder and don't let it idle, lol..


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## likethat (Oct 5, 2007)

Also is the timing set well and does the vacuum and mechanical advance work well. It would run pretty low on power if any of them are not set well or not working right. Is this a points car? I would still guess it is carb.


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## geeteeohguy (Feb 2, 2008)

Two things are going on: your compression ratio is too high, and your mixture is too rich. Leaning it out will make pinging worse, so you're in a "catch 22" situation. A big cam with a ton of duration could be a partial cause for a lot of fuel going into the mix. With a big cam like you have, the car is not meant to idle around or cruise. You should seriously look at a more suitable cam. On today's pump gas, you really want to see a static CR of 150-175 psi. You're right on the edge. I would check the timing curve for too much total advance (you want abut 34-38 degrees TOTAL, use a manifold vacuum source on your distributor vacuum advance, and adjust or repair the carburetor. Running as rich as you are is going to wash down the cylinder walls with unburned fuel and wear out your engine. So: less fuel, less timing, and if that doesn't work, less cam and/less compression. Good luck.


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> Two things are going on: your compression ratio is too high, and your mixture is too rich. Leaning it out will make pinging worse, so you're in a "catch 22" situation. A big cam with a ton of duration could be a partial cause for a lot of fuel going into the mix. With a big cam like you have, the car is not meant to idle around or cruise. You should seriously look at a more suitable cam. On today's pump gas, you really want to see a static CR of 150-175 psi. You're right on the edge. I would check the timing curve for too much total advance (you want abut 34-38 degrees TOTAL, use a manifold vacuum source on your distributor vacuum advance, and adjust or repair the carburetor. Running as rich as you are is going to wash down the cylinder walls with unburned fuel and wear out your engine. So: less fuel, less timing, and if that doesn't work, less cam and/less compression. Good luck.


:agree Your biggest problem is the pinging. If not addressed, you're not going to have to worry about plugs or fuel mixture for very long... 

Bear


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## Dual Tempests (Mar 4, 2010)

Thanks everyone. I appreciate the help. I think the excessive idling is a big part of the problem. It also seems to happen when the battery is not fully charged as the car has a short somewhere. It is a weekend warrior that I usually let idle in my driveway for 15 minutes. Drive around the block and park in the garage... It has MSD 6al, blaster 2 coil, and pointsless MSD or Mallory distributor. The car has Holley 770 street avenger carb on it, and it really does not run any different if I adjust the mixture screws. May have a float issue also, right. I am going o try to lean it out and drive it hard and will let you guys know how it goes. Also, I used to add a gallon of 114 leaded gas to each tank, which made it run great. Any follow up thoughts? Thais to all.


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## geeteeohguy (Feb 2, 2008)

Yeah....Run high octane at all times, and DON'T LET IT IDLE!!!!! Also, the battery is the heart of your car's electical system. If your charging/starting ain't up to snuff, you will have weak ignition and will foul your plugs!!!!


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## 646904GTO (Feb 10, 2008)

Two things in your last post that seem to point to 'over fueling' (notice I didn't say 'rich'). Your condition seems to have come about from a few differnt elements working together. 
1.To high of compression for todays low cal fuel
2. You say it runs better when you add 114 octane
3. Adjusting your idle mixture screws have no effect on idle mixture.
So simply stated you can't run any more timing so you can burn the low cal fuel because it will detonate. When you run high octane it is better because you need less timing to burn good fuel. Your carb is jetted to rich( really just over fueling because there ain't no such thing as 'to rich' if the fuel isn't good enough for the application) because you have no idle mixture control with the idle mixture screws. Now to the spark plugs, I don't think it will matter what plug you use because the low cal fuel/ high compression issue is killing you. Your simple solution short of changing camshafts and installing dish pistons or larger chamber heads is to use a thicker head gasket. Maybe someone in this thread knows the place who makes them. They have a calculator that you can input values and know the compression change.


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## jetstang (Nov 5, 2008)

Dual Tempests said:


> it really does not run any different if I adjust the mixture screws. .


If it backfired it may have popped the power valve, replace it. If it has that big of cam, you may have adjusted the carb out of the idle circuit. You can drill 1/16th hole in the butterflies. Now, with the big cam, you have to open the butterflies to far to get it to idle, thus not using the idle circuit to run the engine. Drill the holes to let the engine suck some fuel from the venturies, then adjust the rest on the idle circuit. If you look at Summit, you can get butterflies predrilled for this issue, and most race carbs are drilled, it's just a balancing act.


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## likethat (Oct 5, 2007)

I had to do it to the 427 on a 750 Holley. It would not run the idle circuit to save its life.


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## Dual Tempests (Mar 4, 2010)

Well. I figured out what the problem was. There were a few things. First, the fuel pressure was too high and pumping tons of gas into the engine causing vapor lock when the engine was shut down. Second, the damn MSD distributor cap was not vented (bad design) and was completely corroded inside) Got a new distributor and fuel pressure regulator and the car runs nicely. Still pings a bit under full throttle when not using race gas!


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