1973 454 Quadrajet Question

[John M.]

All,

I'm trying to understand all of the vacuum ports on a 1973 Quadrajet # 7043201 which is on my 1973 4 speed 454. What is connected to the vacuum port on the right side of the carburetor near the choke pull off? I have attached a picture for reference.

Thanks In Advance,
John

[Joe L.]

Re: 1973 454 Quadrajet Question

All,

I'm trying to understand all of the vacuum ports on a 1973 Quadrajet # 7043201 which is on my 1973 4 speed 454. What is connected to the vacuum port on the right side of the carburetor near the choke pull off? I have attached a picture for reference.

Thanks In Advance,
John

John------


That's usually the vacuum source for the air injection reactor (AIR) system. Does your car have a functioning AIR system? All 1974 Corvettes except base engine with automatic transmission and federal (49 state) emissions certification were originally equipped with AIR.

[John M.]

Re: 1973 454 Quadrajet Question

Joe,

My car does have the AIR equipment. My understanding of the vacuum connection for the AIR diverter valve is that it is in the front of the carb (which is a "t" connection) according to the 1973 Assembly manual?

John

[Joe L.]

Re: 1973 454 Quadrajet Question

Joe,

My car does have the AIR equipment. My understanding of the vacuum connection for the AIR diverter valve is that it is in the front of the carb (which is a "t" connection) according to the 1973 Assembly manual?

John

John------


That could very well be for 1974. My response was more "generic" than it was specific to 1974. However, the capped vacuum port you pictured is the AIR diverter valve vacuum source on many other Q-Jet applications. Apparently, an alternate source was used for your application.

Checking into this further, it seems that the vacuum port you pictured on the side of the carb was used for the spark control system for 1974. This is a miserable system that was one of the roots of many driveability problems with 1974's. It was added by GM as a "stop-gap" system to enable mandated exhaust emissions compliance prior to the introduction of the catalytic converters in 1975. A previous owner may have disabled that system and capped the vacuum port.

[John M.]

Re: 1973 454 Quadrajet Question

Joe,

Just to clear up some confusion (maybe mine), I'm referencing my 1973 car not 1974 as there are slight differences in the carb vacuum lines. My understanding of a 1973 454 4 speed is that the vacuum advance, which comes off the TCS spark solenoid, goes to the back of the carb just above the power brake port. The individual ports in the front off the 7043201 carb are PCV, EGR, AIR diverter valve, and Vapor canister. I cant find any reference to the right side port by the choke pull off.

John

[Joe L.]

Re: 1973 454 Quadrajet Question

Joe,

Just to clear up some confusion (maybe mine), I'm referencing my 1973 car not 1974 as there are slight differences in the carb vacuum lines. My understanding of a 1973 454 4 speed is that the vacuum advance, which comes off the TCS spark solenoid, goes to the back of the carb just above the power brake port. The individual ports in the front off the 7043201 carb are PCV, EGR, AIR diverter valve, and Vapor canister. I cant find any reference to the right side port by the choke pull off.

John

John------


Nope. It's entirely my mistake. I still can't figure out how I thought you were talking about a 1974 when you clearly stated even in the title of your post that your car is a 1973.

It may be that the port on the right side of your carb was unused for the 1973 application and was originally capped. This is uncommon but strange things were happening in the world of emissions compliance in the 70's. I just don't know in this case. I hope we can hear from some folks with original 1973 applications like yours.

[Jimmy P.]

Re: 1973 454 Quadrajet Question

Hello John,
Hope this info helps. I have attached three photos for you to reference. Two are photos from the M.F. Dobbins book,which shows a 454 73 right side carb and the port is capped like yours. So that probably was the case for the 454. I have also included a pic of my L48 showing that a hose goes from that port to the front of my TCS solenoid which on the small blocks is mounted on the right front intake.Also, my AIR hose goes to the left front of the carb as your 454 does. On the 73-74 big blocks the TCS solenoid is mounted to the right side of the coil bracket.
hope this was helpful.

[John M.]

Re: 1973 454 Quadrajet Question

Jimmy,

Thanks for the post. The port in the back of the 7043201 Quadrajet (73 BB) is manifold vacuum and connects to the vacuum advance from the TCS spark solenoid. I would like to know if the port on the right side is ported or manifold vacuum on the 7043201 carb. The small blocks used a different carb and a different TCS solenoid as you know. Did the quadrajets of 73 have similar ports because of production reasons and what was the difference in functionality...the big question in my little brain!

Best Regards,
John

[Joe L.]

Re: 1973 454 Quadrajet Question

Jimmy,

Thanks for the post. The port in the back of the 7043201 Quadrajet (73 BB) is manifold vacuum and connects to the vacuum advance from the TCS spark solenoid. I would like to know if the port on the right side is ported or manifold vacuum on the 7043201 carb. The small blocks used a different carb and a different TCS solenoid as you know. Did the quadrajets of 73 have similar ports because of production reasons and what was the difference in functionality...the big question in my little brain!

Best Regards,
John

John-------


I believe it's ported but I'm not sure of my recollection. Very easy to check. Start the engine and let it idle. Remove the cap. If it's ported there should be no vacuum at idle. If there's vacuum, then it's manifold vacuum.

[John M.]

Re: 1973 454 Quadrajet Question

Joe,

The small blocks have the vacuum advance from the TCS solenoid connected to the right side port of the quadrajet. I'm confused...I thought the vacuum advance was manifold vacuum not ported vacuum?

Thanks,
John

[Joe L.]

Re: 1973 454 Quadrajet Question

Joe,

The small blocks have the vacuum advance from the TCS solenoid connected to the right side port of the quadrajet. I'm confused...I thought the vacuum advance was manifold vacuum not ported vacuum?

Thanks,
John

John-------

No, by 1973 most vacuum advance was operated by PORTED vacuum. You can check by the simple test I described above.

[John M.]

Re: 1973 454 Quadrajet Question

Joe,

The 1973 BB vacuum advance is manifold vacuum as it is connected to the port above the power brake booster port. These two ports are one in the same as they are connected at the base of the carb. So what changed with the small blocks or am I confused?

John

[Joe L.]

Re: 1973 454 Quadrajet Question

Joe,

The 1973 BB vacuum advance is manifold vacuum as it is connected to the port above the power brake booster port. These two ports are one in the same as they are connected at the base of the carb. So what changed with the small blocks or am I confused?

John

John------


I'd forgotten about that. However, I believe the reason was that the TCS solenoid was installed between the manifold vacuum source and the distributor vacuum control. This essentially obviated the need for ported vacuum to the vacuum advance as was used for earlier applications without the TCS system and solenoid. While the systems were different for small block and big block, I think the basic system was the same.

[John M.]

Re: 1973 454 Quadrajet Question

Joe,

Just a follow up. I can't do the manifold/ported vacuum test on my carb as the engine is out of the car right now. In the mean time, I will post any info regarding my quest for Quadrajet knowledge...

Regards,
John