Spark Plug Color

[Kilgon]

Just put in new plugs, plug wires and cap and rotor.  Took for a test spin yesterday of about 10 miles and came home.  Pulled a few plugs today to see how things look and saw something I never have seen before.  Plugs are half white half black.  Pulled two plugs from each side and they are all the same.   I have a 460 with a Holley 750.  Duraspark dizzy with MSD 6A  controller .  New Taylor spiral core plug wires rated at 40 ohm/ft.  Plugs are Autolite  AP45 with .044 gap.  Any idea of what might be causing this and if it's a problem how to resolve it.   Edited - For clarification the porcelain is white on one side and black on the other.  The pictures below are of two plugs.  First two pictures are one plug and the next two pictures are of another plug.  You can see the electrode turned 180 degrees. 

 

[Jeff73Mach1]

Unless you make a hard pull and shut the engine off immediately, plug reading is not as accurate.  I believe the soot is from running cold with the choke on and the white is from it running a little lean after the choke comes off.  I'd probably increase the jet size in the secondarys and lighten up the tension on the choke if you have one.

 

[Kilgon]

Unless you make a hard pull and shut the engine off immediately, plug reading is not as accurate.  I believe the soot is from running cold with the choke on and the white is from it running a little lean after the choke comes off.  I'd probably increase the jet size in the secondarys and lighten up the tension on the choke if you have one.

Not using the choke.  I would think the color would be more uniform all the way around in either case.  I have always checked my new plugs after a 10 mile run or so and have never seen this before.  Don't really have a spot where I can do a pull and the shut the engine off.  

 

[c9zx]

Were you using the same platinum plugs before? Were you using a .044 gap before? Do all eight look the same? I use Autolite racing plugs or standard Autolite plugs gapped at .035-.040 depending on the particular engine combination. I see no need for a 75,000 mile plug in these cars. Just my opinions. Chuck

 

[Kilgon]

Were you using the same platinum plugs before? Were you using a .044 gap before? Do all eight look the same? I use Autolite racing plugs or standard Autolite plugs gapped at .035-.040 depending on the particular engine combination. I see no need for a 75,000 mile plug in these cars. Just my opinions. Chuck

I was using just Autolite 45.  Gap was at .040.  Pulled 4 out of the eight (2 from each bank) and they all look the same.   I thought about the plug being platinum but being the same heat range I wouldn't think that would be a factor.  Was told to go to a little bigger gap because of the low ohm wires.  They said it would give better combustion. 

I'll change the gap on a few of them tomorrow and see what that does.   Just weird they way they look.   I still have the old plugs and wires.  If changing the gap doesn't help I guess I could back track and put the old plugs and wires back on and change one thing at a time to see what seems to be causing it.   Been working on cars for over 50 years and this is the first time I've seen this.   

 

[TommyK]

Drive it hard for a bunch more miles. IMO that's all idle/transition marking.

 

[Jeff73Mach1]

Tommy makes a good point, what rpm is the engine idling at?

 

[Kilgon]

Tommy makes a good point, what rpm is the engine idling at?

Idle is around 950.   Engine has a big cam with low vacuum and is automatic.  Running at 16 degree with all in at about 2300 rpm.  Took it out and ran it hard earlier today.  Will pull the plugs later today or in the morning.  If things haven't change then I will try changing the plug gap.  If still no changes then I will put the old plugs and wires back on as I mentioned earlier and try to work it out from there.  Will update post when I find out more.

 

[TommyK]

Like Chuck I am not a fan of precious metal plugs in the old iron. I would start by putting copper plugs back in.

When you turn the idle mixture screws all the way in does the engine die?

Big cam with low vacuum can often lead to over exposure of the t-slot giving you sooty plugs. If you don't have control of the idle mixture screws try cranking the initial timing up. If that raises the idle you can close the butterflies a little bit and readjust your mixture screws. If that gives you control of the mixture screws (dies when turned all the way in) then you need to sort the timing and then go back to the carb.

 

[jpaz]

I just noticed that your advance is all in at 2300 rpm’s? Isn’t that kinda early? I thought somewhere around 3000 was the target for Cleveland’s.

 

[73pony]

I just noticed that your advance is all in at 2300 rpm’s? Isn’t that kinda early? I thought somewhere around 3000 was the target for Cleveland’s.

+1 was thinking the same thing. 

 

[Kilgon]

Like Chuck I am not a fan of precious metal plugs in the old iron. I would start by putting copper plugs back in.

When you turn the idle mixture screws all the way in does the engine die?

Big cam with low vacuum can often lead to over exposure of the t-slot giving you sooty plugs. If you don't have control of the idle mixture screws try cranking the initial timing up. If that raises the idle you can close the butterflies a little bit and readjust your mixture screws. If that gives you control of the mixture screws (dies when turned all the way in) then you need to sort the timing and then go back to the carb.

Working backwards here.  Transfer slots pre set before carb is put on.  Timing then set at 3000 rpm to 34 degree.  Use timing  to adjust idle as much as possible to keep the t-slots where they  were preset.    Vacuum is at 7 inches in drive (auto trans) with foot on brake.  PV is a 3.5.  Engines dies if idle screws turned in all the way.  PV is good.    Ran it on the express way as mentioned in above post and just got around to pulling a few plugs.   They are looking better.  The previous white area is starting to darken and the soot area has lighten up. See pics.   I think  as you and  c9zx mentioned the plugs could be the big part of the problem.  Never used them before.  Also could be the plugs in combination with the new low ohm wires.  I will run it awhile longer and see how they burn in.  

 

[Kilgon]

I just noticed that your advance is all in at 2300 rpm’s? Isn’t that kinda early? I thought somewhere around 3000 was the target for Cleveland’s.

It is a 460 big block.  

 

[jpaz]

It is a 460 big block.  

Oh, sorry I didn’t catch that.

 

[Kilgon]

Oh, sorry I didn’t catch that.

No problem.  I've been wanting to change springs anyway.  Want to get the curve more toward 2500 to 2600.   Was putting stripes on today.  Have the passenger side to wrap up tomorrow then will redo the dizzy. 

 

[TommyK]

What list number Holley carb do you have? How many turns out are the idle mixture screws? What is the vacuum reading and rpm in gear (if auto)?

 

[Kilgon]

What list number Holley carb do you have? How many turns out are the idle mixture screws? What is the vacuum reading and rpm in gear (if auto)?

Right now I have my 750 dp 4779-7 on it.  Screws are about 1 1/2 turns and vac in gear is 7.  All is okay on that end.  As I stated in my original post just never seen plugs like that before.  I have always used copper and bought the platinum plugs because they were on sale.  I do believe they just take longer to show how they are running.   They are starting to burn in and are looking better.  

 

[c9zx]

What power valves are in the carb? At 7 in/hg vacuum I'd put 3.5 power valves in the carb. The cam must be very aggressive for the combination or not enough initial advance. Chuck

 

[Kilgon]

What power valves are in the carb? At 7 in/hg vacuum I'd put 3.5 power valves in the carb. The cam must be very aggressive for the combination or not enough initial advance. Chuck

Carb has 3.5 pv . Vacuum is 10 in at idle 7 in. in drive.  Cam is  288/294 -  623/623  112 lsa.  Plenty of initial timing.  Idles best with about 16 to 18 degrees at about 900 to 950 rpms.  Drops to about 750 when put in gear.  Car runs great.   Plugs are burning in okay now.  Just never had a set do that before.  As I mentioned in one of the above  post I do believe it is because they are platinum and take a little longer to show how they are burning.     The only reason I got them were because they were on sale at the same price of the copper.  Will see how they perform in the next few weeks.