Odd spark plug wear

[Barrnone]

I am hoping some of you have seen this kind of pattern before and can explain to me where I should be looking for a cause. This is a 350 TBI motor that has gradually started to get intermittent misses, getting worse over time. I pulled the plugs and all 8 of them have a dark gray spot going down the insulator, some with deposits on the spot also. I have attached a couple photos to show what I am trying to describe. These plugs have almost exactly 10,000 miles on them. Thanks for any help.

[Senator350]

increase the carburetor jet size slightly, take out some timing, or go to a colder plug.

from: http://www.dragstuff.com/techarticle...ark-plugs.html

[cdowns]

TBI motors dont commonly have carbs

[primered_junk]

Go to a colder plug, CR43TS ac delco is the factory plug for TBI trucks, as stated above by senator back some timing out of it. On a TBI motor you have to unplug the "timing control module" which looks like a breaker, that is what controls the advance instead of a vac advance. Dead nuts zero timing is "ideal" per GM, but any place between 0 degrees, and 6 degrees after will work. Also make sure there is no exhaust leaks, with plugs like that a burnt valve is a possibilty. The deposits are cause by the wet fuel that lingers around the exh valve in the chamber. If you can burn that fuel, your problem will burn with it.