Hi luke-44,
The plugs look good, to me white is good. What your describing to me sound like bad wires. I assume there new though. Check for a good accelerator pump shot,check distributor for good advance, mechanical and vaccum. What kind of ignition are you running? HEI or points? HEI plug gap .045, points .035. At what RMP do you experiance this problem and at what % of throttle. Sounds like maybe the jets are too small (lean missfire?).
