Hot Rods Any Edelbrock carb guru's on here?

In top right picture you can see the secondary butterflies and weights can't be throttle plates because they are cut off at the back. these same weights and butter flies can be seen in his picture

 

OK, I stand corrected, but that sure doesn't look like the secondary air valves in my pair of 500cfm AVS Edelbrock carbs.
I think the butterflies you are seeing there are ones that measure air flow and control the rise and fall of the metering needles for the gas flow to secondaries and not to control air flow thru them.

 

An AVS Carter or Edelbrock are more like a Thermoquad or Quadrajet, a Quadrajet does primary and secondary metering rods.. The AVS metering rods are controlled strictly by manifold vacuum.

 

And add only on the primary side. Only metering in the secondary are the jets.

 

Low and behold I have a carb like yours, it came on the engine in my 57 p/u, here I had said I never seen one before.
It's a spread bore type, not a ton bigger like a quadrajet but the secondaries are bigger.

 

There appear to be some sort of secondary air doors, but they're not on top of the carb in plain sight, like on a Q-Jet. Instead they're about half way down the secondary bores. Looking down from the top down the venturis they look like regular butterflies, but they're actually on top of the butterflies for the secondaries. In reading as much as I can about these carbs, there seems to be little adjustability in the secondaries. You can adjust the mixture using metering rods and the springs that control the movement of the metering rods, but that's it. There's little if anything that you can do to tune out the bog that happens when the secondaries are aggressively opened. I'll keep trying to learn and tune, but so far I'm not a real fan of these carbs.

 

Did you read about drilling the swing weight to remove weight out of it ?
That was something I wanted to try but there is no calibration chart letting you know what size hole removes how much and does what.

 

Unless the carb is under sized you will most likely produce a bog problem. The thermoquad is a good carb but showed up on cars when they were leaning carbs for emissions. Then guys found it was easy to change the secondary air valve settings. To much air to quick = Thermobog.

 

When Carter was still producing AFB carburetors (prior to the redesign by the F/M accountants that still say Carter), Carter produced a number of different auxiliary air valves with different mass, and more importantly, different angles of attack. There were two basic platforms (wider, and more narrow).

Carter offered these air valves ala carte.

When Carter started manufacturing the aftermarket AFB, ALL of them were calibrated for small block Chevy. Yes, I know there were a few sold for Fords and Chryslers in the early 1970's, but these were small block Chevy carbs with either Ford or Chrysler linkage, and different metering rods. As Carter already offered stock performance AFB's for Ford, Chrysler, Buick, and Pontiac; there was no need to do aftermarket.

In general, the small block Chevy calibration has weights that are too light, and angles that are too aggressive for Ford (other than small block), Chrysler, Buick, or Pontiac.

To make the aftermarket genuine Carters work WELL on anything other than small block Chevvies on the street, one needed to have a donor carb from the target company (Ford, Pontiac, etc.) and change the air valve. For best results, one also needed to change the primary clusters, the air horn, the step-up rods and springs. The air valves needed to be HEAVIER, not lighter, and the attack angle less aggressive.

I do not know if this applies to the clones, and have only posted due to the discussion about air valves. Removing mass from the air valve on the Carters is a losing proposition UNLESS one has maybe an old Pontiac carb (fairly common) and trying to make it work on a small block Chevy.

In the FWIW category, the air valves with the HEAVIEST weights used by Carter in the AFBs............................were Pontiac super duty engines.

The above applies to street-driven vehicles. Trailered race cars, where the usable RPM is say 4000 and above, often have the air valves removed.

There are those that complain that this makes tuning more difficult, I would suggest two things: (1) start with the right carburetor for the application, and (2) unlike spring-loaded air valves, the weighted air valves NEVER go out of adjustment.

As to the AVS Carters with the spring-loaded airvalves and no secondary boosters, the very best thing I can say about them is they brought in LOADS of capital! Virtually all original AVS Carters were thrown away approximately 5 nanoseconds after the car went out of warrenty, or long before. As we had a few of these from buying out junkyard complete carburetor inventories, when the restorers started restored the Chryslers that came with AVS carbs that had been upgraded, the restorers offered good money for the remaining AVS carbs, knowing the car would be a trailer queen, and they didn't have to drive it.

Jon.

 

If the fuel pressure is at 6 psi or below as you say it is, I would take the top off the carb- (it is very easy to do) and I would check that the floats are set properly. I have had a couple Eddys that came from the factory with the floats set too high. After that The step up springs may need to be a little heavier- as someone else mentioned- the carb manual has some great info and Edelbrock has great info on you tube as well.
Not a difficult carb to sort out. Yours looks like a 1406 model- 600 cfm with the electric choke- very common size for a sb Chev To avoid complication and confusion-I would keep my changes to one at a time while I worked through the problem.