White spark plugs and tuning my Holley DP

I haven't posted a tech question in a while, now that I have most of the demons worked out on my new engine.

Only problem is now that I swapped out my shorty Accel spark plugs for Autolite platinums (cheapies from walmart, because they fit on my non-P heads), I cannot get the plugs to run anything other than clean white.

Thought I had a vacuum leak in the carb, but a couple calls to Holley tech say not.

I am only working on the primary circuit at this time. Carb came used with 65/67 jets, but immediately bumped them up to 68/74 when I was messing with the secondary mixture on the new motor.

Now I am running 72/74 trying to richen up the primaries.

Now, it runs great, takes off really nice, scratches when it gets into second (even at only 3000-4000 shifts, not floored), and runs a nice even 180 degrees. In other words, I wouldn't even be messing with the mixtures except for the white plugs.

So, are these plugs just going to run hot or white because they are too hot for the motor?

They are walmart $2 each Autolite w/platinum AP764. I chose those because the little computer at the spark plug aisle said to use these plugs on the 98 Explorer, and the 93 Mustang GT (both cars I knew used GT40 type heads and were 5.0).

So, should I keep messing with the mixture to rich it up until the plugs get darker, or swap to a different and/or cooler plug?

 

first platinum plugs not good for makeing power. they are good for longevity. get the non platinum autolite plugs. just take the ap off the number then you have the regular copper plug. stay with autolite. the white could be deposits from the super high quality gas that we can get these days. Just kidding, todays gas SUCKS. but it could still be deposits from the gas. what did the accel plugs look like when you took them out?

 

The accel plugs had a nice color to them. Maybe a touch dark, but not black, and definitely NOT white. These platinum plugs are new, maybe have 50 miles on them, but I cannot get any color to them. I also bumped up the primary metering jet to 76 (yes, 74 secondary, 76 primary) and still running white.

Do the platinums run hotter?

These plugs have about 6 hours run time on them, most of it idling while tuning, but most recently a trip around town for some shopping, then a little highway driving at just under 3000 rpm for about 10 miles, then home, into the garage, parked, pulled plug. With all the low speed driving, I would expect them to be pretty dark.

 

Do the plugs actually have a white/grey ash deposit on them???Do they look glazed(shiney)If not I would run the engine till you have about 1 or 2 hundred miles on them and look again,hows your timing?I dont think you have a rich condition.If any thing you may need a colder plug.Does your engine ping under load at all?

 

I don't notice any ping. I have never heard it before, and would assume I would know it if I heard it? I had a header leak until today, and finally got to retorqueing my header bolts, and now that noise is gone. Wouldn't I be able to hear ping if I can hear header leak?

Besides, most of the driving I did today was just cruising, not any hard acceleration. I am trying to keep this running only on the primary circuit until I get a better burn. I don't think my secondary is having any problems, as it runs GREAT when my foot is on it (although I have not done a full throttle-and-stop check on my plugs, just part throttle and idle).

The plugs don't have a white ash on them, but just look new. They don't appear as if they have ever been used at all. They are definitely burning off whatever I am throwing at them, so far.

Part of this question was to see if someone knows if these platinum plugs are too hot...

The other part was to see if anyone has experienced this and think it might be a vacuum leak.

 

I dont think you have a vacuum leak.Holly carbs are pretty touchy if you have a vacuum leak any where they wont tune up well.My guess is its a hot plug,that the engine seems to like since it has no pinging or detonation issues.Like I said leave every thing alone if its working to your satisfaction and put a couple hundred miles on it,then look at the plugs.I have had cars run clean plugs and not cause problems,I have also had em ping on me as well from too hot a plug.Also,newer gas formulations dont leave alot of deposits on a plug(no rusty brown color)Sounds like you have a pretty tight well tuned engine right now.Just enjoy it and dont over think it.

 

Well, I DO have one other problem I will need to address, and wanted to get the carb tip-top before I hit it. Also related to spark plug, I think...

At cruise, it feels like it periodically loses spark on a cylinder on the left side. I can hear a dull pop (unfired round) go through the left muffler, on a periodic basis. I think i have a spark plug wire grounding out, or broken. I am 95% sure a new set of wires will fix that, as I have just replaced the distributor cap, rotor, and running a pertronix recently checked to verify the clearance.

One LAST thing on the plugs. I am running a larger than stock gap, would that do this to me? I am running them around .045. Worked well with my Accel shorties, but wonder if they are affecting the platinums somehow. Computer recommended .054, but I thought that was WAY too big. I think stock is around .036?

 

My understanding is you are not supposed to gap platinum plugs manually.They are supposed to be set at time of manufacture.(I have seen many that needed to be gapped anyhow)I would tighten up the gap to 0.30 or 0.35.As for a miss I would think you would feel that at low rpm(idle)more so than anything over 1500 rpm.Could be the case though(bad wire/plug)Are you sure its not leaning out on you up top?The other thing that comes to mind is a burnt exhaust valve or a sticking one.Hope thats not the case!!

 

It could be leaning out on top, that is why I wanted to get the carb working before I swap wires, because the wires are pretty nice and fairly new.

If it was leaning, then that would give me the white plugs.

This is cruising at 2500-3000, not accelerating or when I have it nailed. It runs good when I run it hard, but when I back of and start to just cruise, that is when I feel the "miss".

I have the full fuel calibration kit. I guess if I get time, I can jump up the primary jets to, lets say, 90 and see if the plugs color or it starts to smoke. I think I will go ahead and get the cheap copper plugs and gap them to .035 first, just to remove the platinum variable.

And like I said, the plugs came from the store with .054 and were recommended to be run at .054. No way I am going that big on a barely-better-than stock distributor/coil setup.

 

I wonder if I would enjoy this car half as much if it just ran right all the time

I think most of the fun is figuring out what is messed up and trying to fix it.

Thanks for the help...

 

Did you install a better coil with the pertronics set up??? A weak coil can cause the coasting pop you described.The other thing that will cause the pop is the fact the engine is still loaded when you back off the throttle.Unburnt fuel goes past the valve and gets re-ignited by the next exhaust stroke.Speed and rpm dont jive,more fuel goes into the engine than it needs when you back off the throttle at high speed/RPM.(no need for the fuel but the intake tract and air velocity just give it a bit more before cathing up/slowing down)and POP! Not un unusual.Good luck Scoop.

 

This isn't the coasting pops, even though I get those too on both the car and my truck.

This is a periodic and patternless misfire at highway cruising speeds. Not enough throttle to open the secondaries, but cruising with the primaries open at maybe 90%. It almost feels like a gust of wind is hitting you in front, since you can feel the loss of 1/8 of the engine's power for just a second or two as that cylinder isn't firing. Meanwhile you hear a lower hollower tone on that side of the exhaust (true dual) helping me narrow down where the problem is located. So, not really a POP, but just a dead cylinder sound.

When I had the burned plug boots on my P heads and long plugs, it felt just like this, which is why I am leaning toward an electrical fix, not carb.

I upgraded to the Accel Super Stock, which is a little stronger than stock, but not much. This went in with a new stock distributor. The pertronix came a bit later.

All of these problems are new. New, as in "this week and last week only". Since I swapped the spark plugs. I guess my engine really liked those shorties, or maybe it just doesn't like platinum.

I just can't tell where I am on the carb without reading the plugs. So, until I get the plugs to where they are giving me some feedback, I really don't know what is going on with the carb.

 

Also, I wonder if I didn't damage one of the plug boots when I was swapping the plugs, causing this misfire.

The boots are 120 degree bends, and some are still a bit hard to reach, I could have easily bent one toward 180 as I was fighting to get the boot off, and bent up the snap-ring inside the boot so it won't snap down hard on the plug, or just cracked the inner wire.

 

Change the wires first.One at a time if you want.you can narrow it down that way to a particular cyl.MMM Din- din time! Im hungry.See yah!

 

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

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