Background: 56 TBird with 312 YBlock, ported ECZC heads, EZC 9425B intake, mild cam (Ford's highest lift from a '57 T-Bird, 275/.423"), dual-point Mallory YH distributor with dwell at 31, stock exhaust, timed at 18 BTDC.

A couple years ago I put on a a BG Speed Demon 575 cfm carb. The engine runs real strong, but I've noticed sooty black exhaust residue, and in doing my year-end checkup the plugs look dark. Also, no matter how much I try to adjust the 4-corner mixtures and the idle speed, I can't bring the idle down below about 1,100. (I previoulsy had a Holley on her and was able to idle it at 600.)

I'm thinking the carb's idle feed restrictors are too rich. They are 31's. I calculate that 28's would reduce the flow by 18%. The problem is that I've read the idle feed restrictors are pressed in on a Speed Demon although I haven't taken the bowls off yet. If that's the case I'd have to drill them out, tap the metering block, etc. Then I read that sometimes people try a single strand of stereo wire to cut down the flow, it's a lot easier. That makes sense to me, but what would I hook the wire to?

I also read that when reducing the IFRs, you should drill the 4 idle air bleeds in the carb's main body bigger. Should I do that? or will it mess up the onset of the main circuit?

Thank you.