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C3 Fuel, Emission Control, and Exhaust Systems

Rochester Quadrajet (1/12)
 6/6/18 11:51pm
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

Hi All,
 
I have a question in regards to the carburettor on my 69 427 Big Block Corvette.
 
I was just wondering with the choke open should the air valve lockout lever tang (circle in red) be in that position? In the current position it prevents the secondary air valves opening.
 
I have done a little bit of reading of the Rochester Quadrajet manual and it seems to suggest that the tang should drop back if the choke is open allowing the air valves to open freely.
 
I am by no means knowledgeable on carburettors and just asking for advice.
 
I have previously had an issue where my throttle wasn't adjusted correctly resulting in the throttle only opening 30% resulting in my secondaries never opening. I have adjusted the throttle now to the correct position so it opens 100% when the pedal is to the floor.
 
Thanks for any help and advice.





|UPDATED|6/6/2018 8:51:47 PM (AZT)|/UPDATED|
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Re: Rochester Quadrajet (2/12)
 6/7/18 1:00am
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 554

IIRC, the lockout on mine prevents the secondaries from opening and yes it should release when the choke is fully open.

______________

1973 L-82 4 spd

Re: Rochester Quadrajet (3/12)
 6/7/18 1:46am
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

I am not sure that the choke is fully open by looking at the angle? I am thinking that's why it's not disengaging the lockout?
Does the choke coil/rod look like it has been installed backward? Could this be why the choke isn't fully opening?
Re: Rochester Quadrajet (4/12)
 6/7/18 1:32pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 19638

 First thing...the choke is NOT fully open in that pic. Second thing, what you have circled is the AIR VALVE lock-out. The actual secondary throttle blade lock-out lever is down on the bottom. The design is for the secondary throttle blades to open with the throttle linkage(at 3/4-full throttle), and the air valve is controlled by the amount of air rushing past them with the throttle blades open.....like a variable venturi effect. The air valve assy keeps the engine from bogging down completely when the secondary throttle blades go wide open.
So...first thing I would do is adjust the linkage from the choke coil to the choke lever, and get it to be fully open with the engine warm. Then see if full throttle will open the secondary throttle blades. NOT the air valve( on top), but the throttle blades themselves. If the throttle blades are not opening, the air valve will not move either.
Sometimes, the little lock-out "tang" for the secondary throttle blades will gum up, of otherwise stick, and keep the secondaries from opening. You have to make sure the choke is opening fully when warm before doing anything else. Thumbs Up




|UPDATED|6/7/2018 10:32:16 AM (AZT)|/UPDATED|


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Re: Rochester Quadrajet (5/12)
 6/7/18 6:55pm
73shark
Standard Member
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 554

A good reference source is the Rochester Quadrajet book put out by HP books.

______________

1973 L-82 4 spd

Re: Rochester Quadrajet (6/12)
 6/7/18 6:56pm
73shark
Standard Member
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 554



|UPDATED|6/7/2018 3:56:20 PM (AZT)|/UPDATED|


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1973 L-82 4 spd

Re: Rochester Quadrajet (7/12)
 6/7/18 8:40pm
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

Adams' Apple said:
 First thing...the choke is NOT fully open in that pic. Second thing, what you have circled is the AIR VALVE lock-out. The actual secondary throttle blade lock-out lever is down on the bottom. The design is for the secondary throttle blades to open with the throttle linkage(at 3/4-full throttle), and the air valve is controlled by the amount of air rushing past them with the throttle blades open.....like a variable venturi effect. The air valve assy keeps the engine from bogging down completely when the secondary throttle blades go wide open.
So...first thing I would do is adjust the linkage from the choke coil to the choke lever, and get it to be fully open with the engine warm. Then see if full throttle will open the secondary throttle blades. NOT the air valve( on top), but the throttle blades themselves. If the throttle blades are not opening, the air valve will not move either.
Sometimes, the little lock-out "tang" for the secondary throttle blades will gum up, of otherwise stick, and keep the secondaries from opening. You have to make sure the choke is opening fully when warm before doing anything else. Thumbs Up







Thanks I will start with ensuring the choke opens fully.
With the choke coil, I will reverse this as literature is telling me it is around the wrong way.
 
Also the choke coil cover is missing, I know this has an impact and may result in the fast idle not kicking down when warm?

Re: Rochester Quadrajet (8/12)
 6/7/18 9:10pm
73shark
Standard Member
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 554

Without the choke cover on, I don't think the engine heat will warm up the coil as fast thereby slowing the opening of the choke.

|UPDATED|6/7/2018 6:10:51 PM (AZT)|/UPDATED|


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1973 L-82 4 spd

Re: Rochester Quadrajet (9/12)
 6/7/18 9:14pm
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

73shark said: Without the choke cover on, I don't think the engine heat will ever completely warm up the coil and thereby opening the choke fully.

Makes sense, I don't actually have the cover. As long as the choke closes it is fine, I should be able to just manually kick the fast idle down after a couple of mins?


Re: Rochester Quadrajet (10/12)
 6/7/18 9:42pm
73shark
Standard Member
Send Private Message

Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 554

Yes you can kick it off of fast idle but if the choke is not completely open, it will not unlock the secondaries.

______________

1973 L-82 4 spd