[Jack21]

Ditto on the Speed Demon route. For the 393, use the 750DP. I have a stock displacement 351W. Was running a Holley 700DP (4778) and never could get it dialed in. Swapped it out for a Speed Demon 650DP and the difference was like night and day. Out of the box with no changes, the motor idled better, pulled off idle better, and ran smoother all across the powerband (850 idle - 6200 RPM). Demons do a better job of fuel metering than Holleys do.

That being said, if you're running a hydraulic roller cam and your idle vacuum is in the 15" - 16" range, you're going to have to jet it down to get the a/f right. The rollers pull a lot more vacuum, and send a stronger vacuum signal to the carb than flat tappet cams do.