runs, but doesn't run....

[zipzip]

I have a perplexing problem....

I've run the engine for about 1/2 hour total. It will stay running if I put in the 3000 rpm rev limit chip in the MSD ignition (6AL). If I replace the chip with the 6000 rpm chip, it will start, but not stay running, even if I goose the carb.

I think it may have something to do with an improper carb setup (I got the thing used and don't know where it's set at), but before I tear into it, I'd like your thoughts.

Here's some specs:

-302 engine - pretty much stock but with GT40P heads, and a "slightly" bumped cam - Intake .448 & 204° duration, Exhaust .472 & 214° duration
-Duraspark ignition - 8° initial advance, about 40° total (with vacuum line on)
-Holley 4160 600 cfm, vacuum secondaries, manual choke.
-Weiand 8011 intake, dual plane

I've messed with the idle adjust screws - anywhere from all the way in to 1-1/2 turns out with no change in operation. It will idle up at the rev limit and I can't get it to drop down.

I've read that sometimes a small hole has to be drilled in the butterflies to get idle adjustment to work. What about that?

It smells rich, but the plugs are ok - It's probably because the ignition is cutting the spark at the rev limit.

What to check? What could it be?