adjusting the choke

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Mar 21, 2010 | 08:06 AM

Ruthie76

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adjusting the choke

I have an electric choke on my 76. is there anyway to adjust it. It takes a good 5-10 minutes for it to release after running. I just had the carb rebuilt last summer. It is the stock quad on there.

Mar 21, 2010 | 08:29 AM

midyearvette

Le Mans Master

Joined: Nov 2008

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From: columbus oh

Quote:

Originally Posted by Ruthie76

I have an electric choke on my 76. is there anyway to adjust it. It takes a good 5-10 minutes for it to release after running. I just had the carb rebuilt last summer. It is the stock quad on there.

depending on outside temperature, it might take that long for the choke and fast idle to release all the way, could be it needs some oil spray on the linkage or it is set too rich, be sure there is no sticking or binding on the choke shaft itself....to adjust, loosen the screws on the choke stove on the pass side of the carb ...there should be an indicator showing rich or lean and which way to turn it....just go two notches at first to the lean side and re tighten the screws and try it out on a COLD mill only....

Mar 21, 2010 | 10:48 AM

7T1vette

Team Owner

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From: Crossville TN

If there is a heat pipe going to it (or something similar), you should check to see if it is clogged up with soot/carbon. That is a common fault and will cause the choke to delay its action. Clear out any collection of carbon; the exhaust pressure should do the rest. P.S. You might put some newspaper or rags behind the exhaust outlets when you fire it up [to prevent black "junk" from spraying all around].

Mar 21, 2010 | 11:00 AM

KB9GKC

Burning Brakes

Joined: Jul 2008

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From: Green Bay Wisconsin

Quote:

Originally Posted by Ruthie76

I have an electric choke on my 76. is there anyway to adjust it. It takes a good 5-10 minutes for it to release after running. I just had the carb rebuilt last summer. It is the stock quad on there.

Sounds like the electric choke is working fine, "if it isn't broke don't fix it.

Douglas in Green Bay

Mar 21, 2010 | 02:26 PM

TedH

Le Mans Master

Joined: Feb 1999

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From: Tampa Bay FL

The fast idle (2000rpm) should release with a 'blip' of the pedal. However, the choke may require 2-3 minutes to trip if the car is very cold. There is a correct clock position for the OEM Rochester carb electronic choke. It may vary by model. If you can, ping 'Lars'; he may be available to advise. He is the qjet 'guru' in my book.

Mar 21, 2010 | 05:24 PM

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,384

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From: At my Bar drinking and wrenching in Lafayette Colorado

Quote:

Originally Posted by Ruthie76

I have an electric choke on my 76. is there anyway to adjust it. It takes a good 5-10 minutes for it to release after running. I just had the carb rebuilt last summer. It is the stock quad on there.

What type of carb do you have? The '76 Vette came with a Q-Jet using a hot air choke - not electric. You either have a converted Q-Jet or a different carb installed... If it's a converted Q-Jet you can set up the choke as outlined in my Q-Jet setup paper (available from V8FastCars@msn.com). If you have a different carb, set it up per the manufacturer's recommended settings.

Lars

Mar 22, 2010 | 03:27 AM

Ruthie76

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my mistake. for some reason i thought it was electric. It is original so what you are saying is that it is a hot air choke.

Mar 22, 2010 | 12:24 PM

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,384

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From: At my Bar drinking and wrenching in Lafayette Colorado

The stock hot air integral choke on your carb should be set up and adjusted as follows. This assumes that you have the hot air tubes correctly installed to the carb and to the manifold and that your exhaust crossover is functional. If any of those components are missing or altered, the choke will not function correctly regardless of any adjustments:

Remove the three screws holding the black choke cover to the choke housing and remove the cover. If rivets are used, drill out the rivets.
Crack the throttle slightly open and push up on the choke coil lever inside the choke housing until the choke is closed.
Notice that there is a small 1/8” hole recess inside the choke housing which will appear right below the lower edge of the choke coil lever when you push the lever up. Insert a 1/8” drill bit in this recess and allow the lever to rest on the drill bit.
In this position, your choke blade should be fully closed. If not, bend the choke intermediate rod that comes up through the body of the carb and attaches to the choke blade lever. Bend the rod so that the choke blade is fully closed.
Now, remove the drill bit, crack the throttle slightly and rotate the fast idle cam (the steel counterweight that rotates on the choke housing shaft between the choke housing and the carb body) so that the fast idle cam follower is positioned on the second step of the cam, right up against the edge of the highest step.
In this position, apply light finger pressure on the choke coil lever inside the choke housing to close the choke (lift up on the lever).
The choke should be cracked open 5/16” as measured between the rear upper edge of the choke blade and the rear airhorn wall. Use a drill bit to check this.
To adjust, notice that there is a small sheet metal tang attached to the lower side of the fast idle cam. This tang determines the travel range of the choke. Bend the tang to adjust.
Now, install the choke housing cover to the choke housing. If you’re using an electric choke, DO NOT use a gasket between the cover and the housing. Be sure that the choke coil tang in the cover correctly mates with and engages to the choke coil lever inside the housing.
With the cover attach screws loose, rotate the cover so that the indicator scribe line points straight up. This should fully close the choke. If there is no scribe line (electric chokes do not have lines), rotate the cover counter clockwise until the choke blade is fully closed. Lightly snug the cover attach screws to keep the cover in this position. You may need to crack the throttle open to get the choke to snap closed.
Remove the short piece of vacuum hose attaching the choke pulloff to the vacuum nipple on the carb. Attach a long (about 2’) vacuum hose to the pulloff.
Suck on the vacuum hose to retract the choke pulloff. If the pulloff does not retract, it must be replaced.
With the pulloff fully retracted, use your other hand to lightly push down on the forward lower edge of the choke blade to simulate to force of the air across the blade. This will open the choke slightly. At this point, measure the distance between the forward lower edge of the choke blade and the forward wall of the airhorn. This distance should be ¼”. You can use a ¼” drill bit as a simple gauge to check it. To adjust, turn the screw on the end of the choke pulloff lever. After each adjustment, you must release the vacuum on the hose and suck on it again to re-seat the pulloff, each time apply the light finger pressure to the forward lower edge of the choke blade.
Once completed, loosen the choke coil cover attach screws and rotate the cover clockwise. On hot air choke systems, the cover scribe mark should be aligned with the second dot clockwise of the center dot on the choke housing marks. On electric chokes, the indentation in the outer edge of the cover should be aligned with the screw & clip location towards the forward side of the choke housing. Snug the screws down or re-install new rivets. (NOTE: On riveted applications, the rivet holes can be tapped for #10 screws.)
Re-attach the vacuum hose to the pulloff and the carb.

This completes choke adjustment for an integral choke carb.

Tuning note on Integral Choke Carbs:
When doing custom tuning adjustments on the integral choke carbs, keep the adjustments limited to 2 parameters: Setting the position of the choke cover (rotating the cover) and adjusting the choke pulloff screw. When doing these adjustments, keep the following relationship in mind:

The cover adjustment (rotating the cover) determines how LONG (duration) the choke is applied before fully opening. Turning the cover clockwise shortens the duration. Turning the cover counter clockwise increases choke duration. It only takes a very small rotational adjustment to change this (1 or 2 mark lines on the cover). Contrary to popular misunderstanding, turning the cover does NOT change how rich or lean the carb runs with the choke applied.
The choke pulloff screw determines how RICH or LEAN the carb will initially run when started cold. If your carb runs rich when initially started, turn the screw to open the choke a little more. Likewise, if your car starts lean and wants to die, turn the screw to open the choke blade a little less.

In summary:
Rotate the cover to change the amount of TIME the choke is applied.
Adjust the screw to change how rich/lean the choke is upon initial startup.

Fast Idle Bench Setup:
The fast idle screw is located on the passenger side of the carb, on the primary throttle shaft just below the choke linkage. An initial fast idle setting can be done as follows:

Back out the idle speed screw on the driver’s side of the carb 3 full turns.
Crack the throttle open and rotate the fast idle cam so that the cam follower is on the top (fastest) part of the cam (simply lift the cam all the way up).
Hold the throttle blades firmly closed and back the fast idle screw out until the cam follower just barely looses contact with the fast idle cam. Find the adjustment point where the follower just barely touches the cam with the throttles fully closed. From this point, turn the fast idle screw in 2-1/2 turns.
Re-establish your driver’s side idle speed screw by turning it back in 3 turns to the original setting.
Start the engine cold and fine-adjust your fast idle screw to the fast idle speed of your preference.

Last edited by lars; Mar 22, 2010 at 12:32 PM.