Do I have the wrong plugs?
#1246597
06/07/12 12:06 AM
06/07/12 12:06 AM
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Joined: May 2005
Posts: 127
Missoula, Montana
ChadP
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Missoula, Montana
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Engine is mild '69 440 HP - stock 906 heads, stock intake, 750 Holley DP, stock exhaust manifolds, cam custom grind, but not radical. 10 to 1 compression - about 375 hp. Pertronix ignitor distributor and coil. Only 4,000 miles on engine. Pulls strong, and sounds great. Here's the problem. I put new Autolite AP 85 plugs gapped at .035 2,000 miles ago. Recently started missing under acceleration. At speed, runs smooth...but while accelerating, has a definate miss...even at 70 and you stand on it, it misses. Just put in a fresh set of AP 85's at .035, and it runs smooth and strong, no misses. Some of the old plugs looked like they had oil on the electrode. Engine is burning no oil, no smoke. Gasoline in Montana is 91 octane oxy. I can get non oxy premium across town. Questions:
1. Do you think the oxy fuel is the problem?
2. Different plug?
3. Different gap?
4. Carb not set right?
Any other ideas?
'65 Coronet 500
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Re: Do I have the wrong plugs?
[Re: JohnRR]
#1246599
06/07/12 12:14 AM
06/07/12 12:14 AM
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Joined: May 2005
Posts: 127
Missoula, Montana
ChadP
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I don'tnecessarily want to run Autolites....Want to run a plug that will last for more than 2k miles.
'65 Coronet 500
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Re: Do I have the wrong plugs?
[Re: Cab_Burge]
#1246601
06/07/12 12:51 AM
06/07/12 12:51 AM
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Joined: May 2005
Posts: 127
Missoula, Montana
ChadP
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Missoula, Montana
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Two of the plugs I took out are shiny with oil. Rest are dull. The worst one was from #8. I didn't hear any pinging, but that doesn't mean it's not doing it. So a colder plug will help this?
'65 Coronet 500
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Re: Do I have the wrong plugs?
[Re: ChadP]
#1246602
06/07/12 03:18 AM
06/07/12 03:18 AM
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Joined: Aug 2003
Posts: 43,319
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,319
Bend,OR USA
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Quote:
Two of the plugs I took out are shiny with oil. Rest are dull. The worst one was from #8. I didn't hear any pinging, but that doesn't mean it's not doing it. So a colder plug will help this?
It should, try finding where the oil is coming from, maybe the intake valley pan  Start the motor up and let it idle, take a can of WD40 and spray all around the top of the intake manifold, if it speeds up you found the leak. BB Mopars are famous for sucking oil in from the bottom of the intake valley pans,  Thats harder to find and cure  Usually it takes removing the intake manifold and looking at the intake ports, if there shiny and oily that is your culprit Fel Pro sells some intake gaskets that are .030 thick, probally other companys do also If the oil is coming in the bottom try using a gasket between the valley pan and the cylinder head  Let us know what you find 
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Do I have the wrong plugs?
[Re: Cab_Burge]
#1246604
06/07/12 09:31 AM
06/07/12 09:31 AM
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Joined: Apr 2010
Posts: 4,154
bethlehem pa
mikemee1331
master
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master
Joined: Apr 2010
Posts: 4,154
bethlehem pa
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Quote:
Quote:
Two of the plugs I took out are shiny with oil. Rest are dull. The worst one was from #8. I didn't hear any pinging, but that doesn't mean it's not doing it. So a colder plug will help this?
It should, try finding where the oil is coming from, maybe the intake valley pan Start the motor up and let it idle, take a can of WD40 and spray all around the top of the intake manifold, if it speeds up you found the leak. BB Mopars are famous for sucking oil in from the bottom of the intake valley pans, Thats harder to find and cure Usually it takes removing the intake manifold and looking at the intake ports, if there shiny and oily that is your culprit Fel Pro sells some intake gaskets that are .030 thick, probally other companys do also If the oil is coming in the bottom try using a gasket between the valley pan and the cylinder head Let us know what you find
instead of WD-40 use carb cleaner, no mess!
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Re: Do I have the wrong plugs?
[Re: mikemee1331]
#1246605
06/07/12 09:35 AM
06/07/12 09:35 AM
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Joined: Jan 2003
Posts: 75,102
A Banana Republic near you.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,102
A Banana Republic near you.
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Quote:
Quote:
Quote:
Two of the plugs I took out are shiny with oil. Rest are dull. The worst one was from #8. I didn't hear any pinging, but that doesn't mean it's not doing it. So a colder plug will help this?
It should, try finding where the oil is coming from, maybe the intake valley pan Start the motor up and let it idle, take a can of WD40 and spray all around the top of the intake manifold, if it speeds up you found the leak. BB Mopars are famous for sucking oil in from the bottom of the intake valley pans, Thats harder to find and cure Usually it takes removing the intake manifold and looking at the intake ports, if there shiny and oily that is your culprit Fel Pro sells some intake gaskets that are .030 thick, probally other companys do also If the oil is coming in the bottom try using a gasket between the valley pan and the cylinder head Let us know what you find
instead of WD-40 use carb cleaner, no mess!
and no paint ...
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Re: Do I have the wrong plugs?
[Re: ChadP]
#1246606
06/07/12 10:47 AM
06/07/12 10:47 AM
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Joined: Mar 2007
Posts: 9,336
South-Central (Sebring), FL
Commando1
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South-Central (Sebring), FL
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Quote:
I put new Autolite AP 85 plugs gapped at .035 2,000 miles ago. Recently started missing under acceleration
Not a cause & affect situation here.
From your further descriptions of the problems, it's not the plugs.
1. Carb
2. Valve seals
3. Rings
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Re: Do I have the wrong plugs?
[Re: JohnRR]
#1246607
06/07/12 10:57 AM
06/07/12 10:57 AM
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Joined: Apr 2010
Posts: 4,154
bethlehem pa
mikemee1331
master
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master
Joined: Apr 2010
Posts: 4,154
bethlehem pa
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Quote:
Quote:
Quote:
Quote:
Two of the plugs I took out are shiny with oil. Rest are dull. The worst one was from #8. I didn't hear any pinging, but that doesn't mean it's not doing it. So a colder plug will help this?
It should, try finding where the oil is coming from, maybe the intake valley pan Start the motor up and let it idle, take a can of WD40 and spray all around the top of the intake manifold, if it speeds up you found the leak. BB Mopars are famous for sucking oil in from the bottom of the intake valley pans, Thats harder to find and cure Usually it takes removing the intake manifold and looking at the intake ports, if there shiny and oily that is your culprit Fel Pro sells some intake gaskets that are .030 thick, probally other companys do also If the oil is coming in the bottom try using a gasket between the valley pan and the cylinder head Let us know what you find
instead of WD-40 use carb cleaner, no mess!
and no paint ...
rattle can = you're right
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Re: Do I have the wrong plugs?
[Re: mikemee1331]
#1246608
06/07/12 11:46 AM
06/07/12 11:46 AM
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Joined: May 2005
Posts: 127
Missoula, Montana
ChadP
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Missoula, Montana
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Thursday morning - just checked your responses. Here's another possibility. When engine was first built, was running Mopar electronic ignition. Changed to Pertronix Ignitor and coil after a short time. Did not notice this problem until we changed ignitions. Could it be that the spark is hotter, thus causing the detonation? Still, this wouldn't explain the oil on the electrodes....right? So there's still a problem with that.
Last edited by ChadP; 06/07/12 12:12 PM.
'65 Coronet 500
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Re: Do I have the wrong plugs?
[Re: ChadP]
#1246611
06/07/12 02:41 PM
06/07/12 02:41 PM
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Joined: Apr 2010
Posts: 4,154
bethlehem pa
mikemee1331
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master
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bethlehem pa
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Quote:
Pertronix flamethrower II coil and Pertronix II distributor. Wires are 7mm msd.
that's a pretty hefty coil. you could open the gap on the plugs to at least 40. bigger flame at 40 and you could easily richen up the mix. what vacuum do you pull and what power valve are you running?
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Re: Do I have the wrong plugs?
[Re: ChadP]
#1246612
06/07/12 06:35 PM
06/07/12 06:35 PM
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Joined: Jan 2003
Posts: 16,376
dogdays
I Live Here
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I Live Here
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ELEVATION!!! 3209 FEET!!!!!
You are running a double pumper which is jetted to be rich at sea level. At elevation it has jets at least three sizes too big.
Seems to me that your spark has very little to do with it. The spark is adequate for your engine..
I have lived through a similar problem. Here's my story, which starts out in Denver:
My '64Dog has a poly 318 which was getting poor mileage and fouling plugs right and left. That's not too hard to figure since it was using a quart of oil every 200 miles, or that was my reasoning. The plugs that came out were black and fouled, looked like they were dripping with oil. So I developed a method to clean plugs and could swap them out in 10 minutes or less. When I started to drive my truck over the Rockies, 600 miles at a crack, the problem got worse and by trip's end at least two cylinders wouldn't be working. I wanted to rejet but the stock carb jets are hard to find, so I switched to a 600 Holley. It came with 66 jets in front. I started reducing jet size and eventually ended up at 59s, but the plugs were still fouling. Doggone oil, I thought. Then I bought a Holley 570 Street Avenger used on the 'bay and looked it up. It came with 54 jets in front, so I substituted 52s for altitude. I noticed I was getting much better mileage, like 20% better. And Voila! my plug fouling decreased by around 90%. Now they still foul occasionally but I get at least 1000 miles before the first hole goes dark.
As much as I thought I knew, I didn't realize that running rich could mimic oil fouling so well.
Now on to you. Figure out what jets you have and substitute jets that are 4 numbers smaller. I bet most of your fouling problems go away.
Here's a secret: The ignition system fires the plug at whatever voltage is required to get the spark to jump. So adding a bigger coil or whatever won't
"make the spark hotter". I have used a lot of Autolite 85s and 86s and they are OK but I find that AC plugs seem to work a little better. I like to use an R44S, there are colder and hotter plugs availble, smaller numbers mean colder plugs. I have also used Champions as hot as RJ17YC but they foul earllier than the Autolites.
When you're looking for a plug try to get an extended tip version, they usually stay cleaner. I believe all the plugs I have mentioned are extended tip.
R.
Last edited by dogdays; 06/07/12 06:41 PM.
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Re: Do I have the wrong plugs?
[Re: 1MYTGTX]
#1246615
06/10/12 04:30 PM
06/10/12 04:30 PM
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Joined: Jan 2003
Posts: 27,421
Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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I ran Autolite 74's in my old 906 headed 440 for years. And they were in it for years at a time. I even raced it with the plugs that had been in it over a year and never even pulled the plugs to clean them. I have had very good luck with them and I still use Autolite 3935's in my EZ headed eng in the car now. Ron
Last edited by 383man; 06/10/12 04:31 PM.
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