Just got my June 2008 issue of Corvette Fever Magazine and noticed an article about a beautiful 61 Fawn Biege and White 61 Vette. The article, like most done by CF is excellent, with one possible exception; in the text they take note that the engine is a 245 hp topped off with two "AVS" Carbuetors. One picture shows the engine w/o air cleaner and again they state in the caption that it has two Carter "AVS's". Now I may be wrong, but isn't the AVS designation part of the Edelbrock Thunder Series of Carburetors, with AVS referring to; "Adjustable Valve Secondary"? The picture in the article sure shows a nice set of Carter WCFB's. The owner was quoted as saying that he had an NCRS judge look it over and advise him what he would need to do to prep it for Top Flight Certification. Well, it doesn't look like putting the correct carbs on it will be one them, as I feared when I read the article.
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Re: Dual AVS Carbs on a 61 (?)
The text and captions are wrong, the photo is correct; the author may never have heard of a WCFB.
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Re: Dual AVS Carbs on a 61 (?)
Yes, that is exactly what the terminology "AVS" means (Edit: Exactly NOT; see below), but it IS NOT Edelbrock nomenclature..."AVS" was an original Carter carburetor model designation. I don't think AVS carbs were ever used on Corvettes. My recollection of the service manual description is that AVS means the secondary air valve is spring loaded to open in proportion to the secondary throttle plate opening, and is normally closed for low power demand.
I had one on a 66 Impala small block, 327/275 engine...the car I bought instead of the 66 Corvette 427/425 with side pipes I should have bought.
I talked with my local Chevy parts manager about swapping it for a Holley to increase fuel mileage, but he dissuaded me, saying that changing the carb wasn't going to help. He was right, and, in retrospect, the car actually didn't get bad mileage for the time.
Edit: Mike Hanson is correct, AVS stands for Air Valve Secondary; my mistake...I misread the original post.Last edited by Chuck S.; April 17, 2008, 07:45 PM.Comment
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Re: Dual AVS Carbs on a 61 (?)
Can't say I know much about the AVS carbs, but they seem to be marketed as a performance feature. From past experiences with what we used to call Vacuum Butterflys; we used to pull them out for better air flow through the secondaries (now we are talking drag race cars with low gearing that could use all the dump you could give them w/o hesitation). It was easy to remove them on WCFB's, but on Rochesters, you had to take them out of an assembly that was sandwiched between sections of the carb, then replace the assembly w/o the butterflys in order to maintain the venturi path. I made one up for a 56 Chevy I had with a 58 Fuelie engine, even finished off the venturis with shaft plugs, etc. Well, in the center of the assembly they had a pin that served as a spring stop that was held in place with a lock screw which I thought I had secured well with Loctite. You guessed it, the pin came loose when I rounded a corner, dropped down inside the engine breaking every ring land on #8 piston. Now were'nt I smart?Comment
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Re: Dual AVS Carbs on a 61 (?)
The original Carter AVS is a cousin of the AFB, but the secondaries operated on the "constant vacuum" or "constant velocity" principle like an SU or the secondaries on a Quadrajet.
IIRC it was only used as OE by Chrysler because by the time it became available in the mid to late sixties, most GM applications were using the inhouse Q-jet.
I think AVS stands for "air valve secondary".
DukeLast edited by Duke W.; April 17, 2008, 04:48 PM.Comment
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Re: Dual AVS Carbs on a 61 (?)
The writer from Covette fever, Jerry Ross, wrote the text on nearly every article in the magazine. So, I guess we can go easy on him for this one mistake. He had a lot on his plate. All the photos for his articles were done by Jerry Heasley and they are top notch. In general, I think Corvette Fever does one of the best jobs covering C-1's thru C-4's that there is. Let's face it, we are a shrinking market in compared to the C-5 and C-6 group. So, I guess we should appreciate their attention while we have it.
StuComment
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Re: Dual AVS Carbs on a 61 (?)
Come on Jim! Give them a break. Have you seen the new 63 - 64 Judging Guide? There are mistakes in there that have been carried over for many years. Good thing we know what most of them are. Every now and then we will drag that book out in the years to come to check something and pause; "Oh! Really! Is that the way it is?" and we'll get on the computer like I'm doing now to ask our friends on the Technical Discussion Board in order to get the straight skinny. Right ?
StuComment
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Re: Dual AVS Carbs on a 61 (?)
I don't know about earlier or later years, but in 1966, the Carter AVS was used for Chevrolet, Chevelle, and Chevy II on one SBC engine...327/275 hp.
Interestingly, the carburetor application chart shows Rochester 4MV and Holley 4160 (WTH?) carburetors also being used on the 327/275 hp engine in all three car lines. I can't imagine why they would have used a 4160 Holley on the 327/275 hp. Big block 396 engines in 325 hp, 360 hp and 427/390hp used the 4160 Holley, and the 427/425hp used the 4150 Holley.
For that model year, the 327/275hp was the sole application for the Rochester 4MV...this may have been a midyear running change, specific only to some car models, or the Carter may have been used as an alternate supplier. Since the Carter AVS is covered in the 66 Chevrolet Chassis Service Manual, I assume it was a planned application before the model year started.Comment
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Re: Dual AVS Carbs on a 61 (?)
Fellows;
I guess my comment about working on a 56 Vette with side air adjustment screws went unnoticed on the thread about WCFB's. Has anyone out there got a 56 that you adjust the idle speed with Air Bleed Screws on the sides of the carbs? The system was just like the Caddy El Dorados, only they ran both primaries together instead of 3 stage progressive like on Vettes.Comment
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Re: Dual AVS Carbs on a 61 (?)
Thanks John. That clears that up for me. Thought for awhile there that I was only dreaming about it. Did the Corvette version of this type Dual WCFB's still use the 3 stage progressive linkage? I know the carbs set up that way on Caddy El Dorados used a 2 stage, i.e. both primaries together, then both secondaries, and that probably explains why they idled them both. With the 3 stage it was probably redundant. I used the Caddy quads with adapters on my 57 Chevy for drag racing when I was looking for a few more MPH through the traps. They did provide some unusual torque characteristics off the line though and I used to break distributor rotors when I got a wheel hop going.
Thanks again.
Stu FoxComment
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Re: Dual AVS Carbs on a 61 (?)
Stu -
All Corvette 2x4 setups used progressive linkage with two settings. The factory setting ran only on the rear carb until half-throttle, when it engaged the front carb and the linkage geometry pulled the front carb open faster so both carbs reached wide-open simultaneously. If you moved the front carb link to the upper hole on its lever, both carbs moved together from idle on up. In either case, the idle systems on both carbs operated all the time - both had idle mixture screws.Comment
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