You are in the transition slots. I would definitely check float level/float saturation/pump psi as the black plug as you know is is beyond pig rich which is killing mileage & will wash the cyls. I missed if your initial is in the ballpark. EDIT maybe the excessive idling/goosing the throttle has blackened em to some extent but first I would get your initial up to 15 or more (I run 18 on a bone stock 85 318) with the stock cam adv 4 degrees.