Opinions-Spark Plug Reading

[gsjohnson]

I've got a 1000 miles on my new motor. 2.0 with Webers, E PCs, and DC30 S mod cams. MSD with NGK BP7ES Spark Plugs. It has been running beautifully for the last 1000 miles. This morning when I started it, it acted like it was running on 5 cylinders and it wouldn't idle. I played with the idle mixture screws after it warmed up, but to no avail. I took the car out anyway thinking it would clean out. The car intake misses on light throttle and won't hold a freeway speed with out popping and missing. I put my foot in it and runs like a raped ape with no issues. Here's a couple of pics of the plugs I pulled when I returned from my morning run. I've got my opinion, but I'd like to hear your opinions...

[Flieger]

There not all optimal. One looks like it burns a bit of oil. 2 look lean to my non-expert eye.

[Mr9146]

You try cleaning the idle jets?

If everything was fine, then it wasn't, that means something happened. If the car runs good on the mains but pops and misfires at part throttle that leads me to believe you probably have a dirty idle jet. Tweaking mixture screws wouldn't really correct a problem that just "popped up".

As an aside, it looks like you need to richen up the mixture across the board...but reading the tip of a plug on an Internet photo from my iPhone is a worthless exercise.

[gsjohnson]

That's close to what I thought Marco. Today I installed new spark plugs and reduced the gap from .052 to .048. MSD calls for increased spark plug gap up to .055. I then removed the idle jets and the idle mixture screws one cylinder at a time. Since they are fuel flow connected, I sprayed carb cleaner in each open port alternating a couple of times and then followed with compressed air in the ports. You could see the mixture screw ports exiting air and carb cleaner when compressing air thru the idle jet port and vise versa. I then separated the idle jet from the holder, sprayed and cleaned the orifices with compressed air. I then cleaned and brass brushed the mixture screws, removing the carbon deposits from the tips. Other than that, the tips all looked as they should. I reinstalled the mixture screws with a starting point of two turns out from the base tightness. I was careful not to over tighten them, avoiding damage to the tips. I repeated this step 5 more times. All of this is very accessible with the carbs still mounted. I must say I didn't find any debris in the idle jets or their ports, but there easily could have been a minute piece of dirt that I couldn't see inside the port.

It was time to find out if I really know what I'm doing... I turned the key and it fired right up...a little popping at idle, but it was idling on all six cylinders. Certainly a good sign from how it was running previously. I let it warm up to about 175 and then began to adjust the idle mixture screws...turning them in until it degraded the idle...then I backed it back out a turn. Again I repeated it 5 more times for each port. I was sure it would take another couple of readjustments after I took the car our for a run...And it did...I had to go over the mixture screw adjustment two more times. I then reset the total advance from 31 to 29 degrees to see if I could cool the cylinders down a little bit, so it won't burn so lean. I probably gave up a little poop, but I want the engine to last.
The car runs great, like it did before...My unisync was cracked, so I couldn't adjust the air screws or the side to side balance, but the air screws should be close from when I originally rebuilt the carbs.

[savaden]

Embrace the 20th century, get a synchronizer. . I know, I still use my Unisysn occasionally. You probably had a bit of crud in an idle jet, and just loosening it let the crud move through the system. An idle jet can also be plugged with a drop of water.

With today's unleaded gas, plug readings are about useless, unless you have that dreaded oil burning situation. Normal running will leave black sooty deposits. You can only really check the mixture by running full throttle, shutting the engine off immediately, and then pulling the plugs, but there will be little to no residue to observe. Nowadays, mixture is checked with those AFR meter thingy's. All high tech and such.

SV