It is BESTer to be uNder-carbed ...than "over".

You have received a lot of good advice here but I think I have a good, simple cheap solution to your problem. Instead of spending money on another intake/carb, try this first. In the 80s we were all worried about octane and began building low compression engines, (like yours). We made matters worse by adding a cam that increased duration. This combination KILLED cylinder pressure and performance.
Buy a timimg tape, get out your timing light and a vacume gauge. Install the tape and check with your light to see where your INITIAL advance is AFTER unhooking your vacume advance. Hook the vacume gauge to a manifold vacume source and see where the timing is. Also note the vacume reading. With the engine warmed up, begin to increase advance. The vacume gauge should increase rapidly to a point. Check the advance when the gauge slows down its reaction to more advance. Check your timing at that point. I often found that I had to increase initial timing by more than 10 degrees above the factory setting for the gauge to quit climbing. At this point, check your total advance by revving the engine and reading your light/tape. You should be no more than 36 degrees. If it is higher than that, you will need to limit it in the distributor. Before you quit, shut the engine off and make shure that it will start hot with no problems. If it "grunts", back down the timing until it will start normally. Then check total timing again. Reducing the total timing is simple with a Mopar electronic distributor. It uses Mallory parts available at Summit for cheap. It comes with tabs that tell you what mechanical advance they provide. Simply choose one that comes out to 34-36 degrees when you add your new initial timing amount and install it in the dizzy. Reinstall the dizzy and double check your timing. Now, REINSTALL the vacume advance to the dizzy! Part throttle cruise (where you do most of your street driving) requires LOTS of advance! That is why the factory put the vacume cannister on your dizzy. Make shure that it is working with your timing light and tape. You should see a BIG improvement in your gas mileage. I used this technique to take "hot" setups that wouldn't spin a tire on ice and turned them into tire fryers! I was also able to knock down almost 20 mpg with 440 cube engines and low 3 series gears in heavy cars "in the day".

There had been a lot of good advice given here, already. I would just like to comment on a couple of things I have read.

First, do not put an 850 on it and do not use 38* advance to start with. 30*-34* to start will be tons.

69 Coronet R/T. 440. 3:54 Dana. Keisler Tremec. 850 Demon. Edelbrock Performer. 9:5:1. TTI's. NGK's. Proper tuning with FBO/MSD. 415 hp rear wheel dyno. Low teens highway.

Stock open chamber 440 heads will run best at 38 degrees total advance at 3000 rpm plus whatever vacuum advance. This is the collated result of 10+ years of reading dyno articles, posts, etc.
You really need a high performance curve in your distributor. That will allow more initial advance whle limiting high speed advance to the above-mentioned 38 degrees.

An Edelbrock Performer RPM should be on your buy list, it's worlds better than a factory intake, if you can fit it under your hood. Drop base air cleaners were made for this problem.

The 750 Edelbrock has a very checkered past. There's a reason that most of them sell used on the 'bay for $75 or less. But, if you have not rejetted your carb you have a huge problem. Manual choke Edelbrocks are set up rich for sea level at the factory, because the feeling is they will be used for drag racing. At 5800 feet your carb is probably at least 4 stages too rich. Living in Lakewood, CO I had a 600 Holley on my ride and I'm down from 65 or 66 jets to 60s on the front. So you need to go to the Edelbrock Web page and figure out what you need for four steps leaner. That should get you started in the right direction. If you're going to throw that carb away throw it in my direction, I need a body. But you can probably tune it to work a heck of a lot better than new.

My Golden friend's son traded a 600 Holley that had been tuned for a 625 Edelbrock manual choke carb and immediately lost 5 mpg. My friend worked and worked on the jetting until the car ran good and mileage was back up, and I think he may have gone even more than 4 stages leaner.

R.

My Charger had a 75-ish low comp 440 with 1 7/8" headers, 3" mandrel exhaust, elect. ign. (with a REAL curve in the distributor, and that is a BIG deal), and it had a Holley 750 vac. secondary with a custom fitted K&N stub stack. I had that thing perfectly tuned/jetted and it ran very well for what it was, and then i added a Holley Street Dominator intake (highly recommend!) and suddenly i had to jet up to 80, from a happy 72 (which i believe was jetted up from the stock high-60's?).

The Stub Stack 'adds' CFM, or at least the effect, so my 100K + mile low comp New Yorker 440 actually wanted MORE carb than a 750. No head work, no cam (stock non-HP cam... ugh), no compression. Dont go with anything under a 750 carb. Tune that engine.

Excellent advice here, esp. the post from Hemi Ragtop. You need well over 50 degrees at light throttle / cruise to get anything close to complete combustion. THE SPARK CURVE HAS TO BE CUSTOM TAILORED, except for a drag car, which can almost get away with fixed timing.

I would have much preferred to see a "demand" type carb on there, EG: Edelbrock (or old Carter) AVS, or T-Q. Later 440s, even smog motors, all had 850 T-Qs, and even 318 cop cars had 800s! And then there was the 6-BBl...

The carb's gotta be tuned. GOTTA. What I usually do is disconnect the secondaries totally at first. Ideally you will, at least temporarily, hook up a UEGO sensor / display gizmo. Shoot for 14.7 - 15.0:1 at cruise, 12.5-13.0:1 at WOT. Then do the same for the secondaries.

I'm always amazed that guys will assemble a combo with parts from a bunch of different manufacturers, do almost zero tuning, then be surprised when the "tune" isn't spot-on! The factory spent hundreds, probably thousands, of hours on each combo, and, when the cars were sold, it was still a work in progress!


Rick E.

Why does the vacum increase when the timing is increased? Is it because the RPM of the engine is increasing with the added timing? Just checking