Well I am glad you did the jet change as for sooty plugs, 69 are not going to do that IMO ,what is your vacume reading at idle in gear if you have an A T may your power valve is to blame,but you said turning in the mixture screws in it would die this is what you want,any chance your breather lid is to close the the bowl vents .Have you talk to Holley tech about this problim.
