I read quiet a few posts and searches so i'am hoping some one can help me out . The pic's are not that good then my battery died but i think it is a start . The pic's are from #1 an #3 cylinder spark plugs the easiest to get at . I had a set of NGK TR5's an the ground strap was pure white diffenately to hot so i had some good used R42LTS and made a big difference . On #1 plug shows the discolour on the ground strap , from what i read is good . #3 plug harder to see discolouration but it is alittle lower on the ground strap from #1 . From what i have read an seen i think i have to go one plug colder to make a happy medium . I used a bright light with a magnifing glass an i see no black spots or silver but i have not cut one off yet to look at the fuel ring . These results are from idle an crusing an by looking at the top of the base ring looks like idle is alittle rich . Their is alittle more to this story on how i got to this stage so i made a short version .

 

Run as cold of a plug as you can. If you go too cold, the plug will foul up because it can't burn off the deposits. Having high compression or power adders means needing a colder plug.

Plugs are cheap. Try different heat ranges. A new plug is easier to read than a used plug. Don't waste money on gimmicky plugs. Those Delcos will work just as well as an expensive plug.