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Old 12-26-2011, 06:00 AM
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Originally Posted by 396chevelle
I was wondering if you guys could take a look at these plugs and tell me what you see needs adjusting. I'm confusing myself. There are a couple that are black and the rest are brown like you see in the pic. #3 was dry at the tip, but a little wet on the threads (fuel). All other plugs were pretty much dry. Should I go a step hotter on the plugs. These are a new set of plugs That I put in after I adjusted A/F on the carb for highest vaccum. The only thing I've done different after that was change the module out in my HEI. By the way this is a brand new 496 that I'm still working the bugs out of. I started to get a slight surge when I stop at the light, which is what made me check the plugs. I checked for vac leaks also before I pulled the plugs to see if that was causing the slight surge. The carb is a Holley 4150 850cfm double pumper. Any advice is appreciated! Thanks,
Plug on right looks to be burning about right. The one on left looks to be carboned up like from idling. Intake design/type can effect the a/f distribution enough at low speeds to cause the plugs to look quite a bit different. If the engine is allowed to idle, what you're seeing then is the idle a/f ratio more than anything else.

If you want to get a better idea of the air/fuel ratio, you have to do a "plug chop" to show you the color. This would be done at the RPM/load where you were interested in checking, i.e. if you want to know what the a/f ratio looked like at WOT, you'd run it at WOT to do the chop. Same thing for midrange cruise, etc. Idle mixture can be checked in various ways, but before doing any of that, the timing should be dialed in. Depending on the cam you might need quite a bit more initial timing than would seem 'normal'.

There are instances where the carb is jetted differently side to side, called "staggered jetting". So it will help to know what the cam and intake specs are and under what conditions were the plugs above being used.
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