I have a 440 w/ a Holley model 4150 0-80770 vacuum secondaries using the heavy spring; jets are 74/78; power valve 6.5 window type; primary metering plate 5271 on left side,right side 5275, underneath 3; secondary plate 11166, underneath 3; 30cc accel pump; primary discharge #25; fuel mixture screws set @ 1 3/4 out. Prior to what happened, carb worked fine. Here's timing if needed for diagnosis, this is with the iron heads: 18 degrees initial; 18 degrees in the distributor. This timing worked for my engine w/ 9.5 CR using premium. Vacuum was 15-16 in neutral; 13-14 in D. Timing is set using vacuum method.
Here's the situation. Installed aluminum heads on engine; had to reset distributor to start engine. I followed the instructions in a BB Mopar manual I used. Had the oil gear slot parallel to cam; engine would not start; the engine was fighting itself. Played around with the oil gear slot, moved the wires around ccw on the distributor. Engine fired but backfired and flamed out through carb. Put wires back to factory setting, engine fired up. At this point idle was 1000rpm, set fuel mixture screws out 1 1/2 turns just to get things going, lowered to 850 with car in D. Was setting the timing, engine stalled. Re-fired engine, idle was high, 1200rpm. Reset idle to 850rpm, went back to timing in D. Engine ran ok meaning it idled smooth, when carb was blipped no hesitations; did not road test. Turned off engine, re-started engine, rpm jumped to 5000rpm, no matter what I did couldn't get idle down. Turned fuel mixture screws all the way in; turned idle screw all the way out. First thought, I blew out the PV. Had a spare one (6.5) and installed. Started engine, again rpm jumped all the way to 5000rpm. I seriously messed up the carb. Does it sound like it can be rebuilt? Or is it a paperweight? I have a rudimentary knowledge of carbs, can rebuild one, but am no expert in the finer details.

the throttle blades would have to be wide open for it to be running that high, maybe the secondaries are stuck open?

If the carb needs rebuilt, you can get a hold of Scott Smith Harms, a member here. Or http://www.harmsauto.com/

Rapid Robert-does that mean the vac secondary pod that operates the secondaries has blown out causing them to flap open?

Rapid Robert-does that mean the vac secondary pod that operates the secondaries has blown out causing them to flap open?

no, if the diaphram blew the secondaries would never open. But if the backfire bent any of the four throttle plates then it can stick open.

You don't need the secondaries to hit 5000 rpm in park.

You don't need much throttle opening at all to be honest, there is no load.

Make sure the throttle is returning to closed and nothing is keeping it open

A Holley 80770 is one of their Street Avenger carbs and I am pretty happy with my 80570. You can easily rebuild the carb. You may want to replace parts with better versions of the part.
As you know the Holley 4150 is a modular design and every single part is available from aftermarket vendors. For those who don't know the 4150 is a line of square bore carbs that have a primary and a secondary metering block. Most have center hung floats and an inlet on each fuel bowl. The 80770 is rated at 770cfm.

I think what happened is during one of the backfires there was damage to the throttle system. Some or all of the blades were bent or the vacuum secondary system was damaged and this allowed the secondaries to open and stay there.
With secondaries wide or partially open the boosters in the secondary bores are seeing airflow and start metering fuel. You cannot stop it by doing anything with the primary side of the carb. You could actually disconnect the front primary fuel bowl and the engine would still run.
It's like a runaway Diesel engine as the only way to stop it is to block the air intake. You can buy a completely new Quick Fuel throttle assembly for less than $130. You can buy a used 770 for around $250.
If you switch carbs you could sell the damaged carb here and get some $$$ back.
R.

I'll check the throttle blades and see if secondaries are hung open. Didn't think of those components. I'll check on them and get back if they don't solve the problem. Thanks for your replies.

Holler what it turns out to be.