71 Challenger, 2.76's, 27" tires.

Stock 5.9L Magnum with RPM airgap. Idles at 20"Hg, Timing is 16° - 35° by 2800, Vac advance is in use

Carb: Slayer 600 VS

PV - 8.5 (was 6.5, too much throttle required for enrichment)
PVCR - .041 from .052 (was dropping from 14:1 to 11:1 at open, now drops to 12.2)
Mains - 70 (was 68)
Secondaries - 71 (was 74)
IFR - .028 from .031 (was only 1/4 turn open on idle screws, now 1 1/4)
Spring - Brown (second stiffest), was yellow
Bleeds - should be OK, AFR does not drop or climb through the RPM band during light accel.


-Idles at 12.5:1 at 650 RPM
-Moderate Tip-in still has a hesitation with the pink and orange cams, even though accel pump squirt is instant.
-Off idle through 2800 rpm stays between 14:1 and 15:1 as long as acceleration is light, staying above about 10"Hg.
-Cruise is 80mph at 2800 rpm, 18"Hg. running about 14.5:1. Smooth and happy.
-Moderate acceleration (~5"Hg.) causes a nasty, sustained bog above about 2000. AFR reads 12:1 and runs TERRIBLE unless I go WOT. It will sustain this bog as long as I hold about 5"Hg, which is easy considering it can barely accelerate since it is running so bad. If I go WOT, it clears up in about a second and pulls very nicely to 5000 and maintains about 12.5:1. The secondary spring is brown, the second stiffest, and it made almost no difference over the soft yellow. I haven't tried the black one yet.

The mid-range bog is about to drive me to EFI. I can't leave a stoplight at anything other than Grandpa or Punk Kid, and it lean pops no matter what at tip-in. Passing a slower driver results in a sustained bog/backfire unless I go WOT to get out of it.

Ideas?

Sounds like typical secondary bog, but I'm almost topped on the springs. I have LOTS of vacuum, but vac secondaries are tied to velocity thought the carb barrels causing vacuum under the venturis, not manifold vacuum.