Last Fall, I changed the stock rods and main jet in my carb (Edelbrock 1406) in hopes of coaxing more power out of the engine. This is #9 on the reference chart (.095 .073/037) I hadn't fine-tuned this motor since the rebuild a few years back. The throttle response seemed significantly better, especially when stepping on it while cruising but there was still just a hint of hesitation. I had .101s in the secondaries so I dropped down to .098s. Still no change. I was happy enough with the change that I left it for the winter.
About a month ago, I drove it for the first time in a while. It was a dog. There was a big stumble when revving at idle and it stumbled all over on the road. When getting on it from about 50mph, I had a big pop in the carb so I granny'd it home. Digging in this past weekend, I found plugs 2, 3, 4, and 6 looking blue/green as in the pics:


I assume the plugs are now junk. Is this from a lean condition?
I pulled the carb and am checking all measurements to ensure those are correct. I'm confirming my timing again as well. I think I'll go back to .101s in secondaries and move to the top hole for a little more shot on the accelerator pump. I have the silver (most firm) step-up springs. I'm not really sure where I went wrong, given that things seemed much improved before the temp dropped.
The engine is a 400 with TMeyer pistons, CR ~9.1:1, stock heads/Performer intake, medium cam and MSD ignition all around. Everything is virtually new.

 

Odd, did yuou use a fuel cleaner or additive?

 

Nope

I've heard these carbs are really sensitive to fuel pressure. I have a regulator and it is set right at 5.5psi so that should be another variable out of the mix.

 

I don't know why you got the unusual coloring on half of the plugs. I'm assuming that the others had more conventional coloration. The plugs may not be "junk". If you have a spark plug tester/cleaner, give them a cleaning and then see how they spark. Compare the ones with unusual coloration to those with conventional coloration.

 

Blueish or green deposits on plugs sound like copper burnt on, like a penny in a torch's flame.

 

How long has the gas been sitting in the tank?

Also if you have a bog off idle changing the secondary side dose nothing.
Make it so the secondary side will not open and adjust the primary side till it is good then adjust secondary side.
Dave ----

 

I agree copper could turn them blue but how did it get into the combustion area?

 

Spark plugs have copper internal conductors and copper electrodes, even some use plated copper. When the plating is gone, there's copper. One thing that will kill plugs is heat from lean burns or too hot plug heat. Plugs are designed for heat ranges, how hot they are is determined by the porcelain insulator and the path to the outer body where excess heat is dissipated. The further up inside the plug that you can see the insulator, the further heat must travel to be dissipated, the hotter the plug tip will be.

 

I agree but, the electode looks fine, no wear on it.

 

If were me ... I'd try a set of Autolite AP-25 plugs in it. I know the theory behind those plugs, but when that coil fires and a spark travels through the wire into the plug, it's looking for the nearest path to ground. It's not gonna care which side the last spark jumped to ground, it's gonna hit the closest or best path it sees.

 

I don't think E3 uses copper on the electrode tip. At least it doesn't look like it. I've used them for a long time.

 

They may not, or maybe it's plated with nickel? If the plug is running really hot like overheated (leaness of mix, wrong heat range, etc) ... AND ... if the center conductor is copper to the tip ... then some copper would extend into the combustion chamber in the porcelain ... would it then be possible? I'm not saying it is the cause, just trying to account for color of deposits.

I've never run E3s but I know many do and are happy .... I'd be curious to do some filing to see if there was any copper under plating or etc.

 

X2
Our trucks were made to run the old type of plugs and run pretty good with them.
My .02

I dont remember if you said or was asked what you running for the IGN system?
Points, DSII, other?
Dave ----

 

I had time off leading into the holiday weekend and have been very busy and not near a computer.

I've got a MSD 6AL running a 8477 distributor. Gas is probably a few months old but I try to keep Stabil in it if I'm not going to drive it.

Before this, I corrected a vacuum leak and I'm uncertain as to how long that has been there and if it aligned with the last time idle mixture screws were set. The timing mark on my balancer was off so timing is yet another thing to confirm. My secondaries were opening way too soon. Spec is 1.3cm and mine were opening at 1cm. I still can't explain the plug color but I clearly have a variety of things working against me. I can't wait to get this sorted out and see the difference.

 

Timing off, vacuum leaks maybe too, lots of room for plugs overheating there. And if over heated, if the electrodes are plated over copper ... well