I changed out the plugs in my `84 K20 yesterday. Plugs were R44TS; 3 plugs came out with chocolate colored tips, 3 came out gray/white, 1 came out white and the last one came out with crud on it almost like it was running very rich on that cylinder. The white plug came out of #5 and the cruddy plug from #6. Here's the engine... 350 bored 30 over, flat top pistons, 76cc heads with large valves. Edelbrock 650 cfm carb on an Edelbrock Performer intake. Headers & 2.5" duals. Maybe 3-4k miles since I rebuilt it. This is the third time I've replaced the plugs since the rebuild (first two sets were R45's, last set was R44's, put R45's back in yesterday) Basically the truck runs excellent with fresh plugs... then after a little while (500 miles or so) performance goes down hill and power surges during acceleration. Does this sound like a carb problem... like a rejetting issue? The plugs tell me it's running lean on some jugs fine on others and I don't know what all that crud came from on the other plug. Thanks for any help.