Cable Adjustments for Carburetor Secondaries

[fine69]

Hi All.

First, keep in mind that my rebuilt engine has not yet been fired up.

I utilized my stock bracket to connect the throttle cable to a new Edelbrock AVS 650 cfm carb. When I move the throttle assembly by hand, I can get the secondary blades to open. The problem is that when I depress the accelerator pedal, the cable doesn't pull the throttle assembly as far as when I do it by hand - the secondary blades don't open.

I'm thinking that this a problem with the cable length. If this is so, is there a way to adjust the throttle cable?

 

[George Black]

This is a fairly common problem and can be fixed. First, be sure the problem is with the linkage and not with another aspect of the carb.

With engine off, have someone sit in the car and push the gas pedal to the floor while you observe the throttle linkage on the drivers side. When the pedal is to the floor, grab the linkage and see if it is wide open or if it has more travel than the gas pedal allows. If short on pedal travel, there are several possible fixes.

(1) If you used the stock metal throttle linkage bracket that is attached to the rear of the carb, simply adjust the throttle cable. The cable is attached to it via a tubular clamping bracket. Loosen the clamp, slid the cable 1/2 inch or so, retighten the clamp, and check operation of the linkage. (One person in car pushing on accel. pedal, other watching the linkage travel). A very minor adjustment of the cable in the tubular clamping bracket makes a BIG difference and usually solves the problem--especially on Q Jets--but should work on your Edelbrock.

Other possible fixes include (2) bending the metal linkage throttle bracket that is attached to the rear of the carb; or (3) bending the accel. rod under the dash so that you get full movement of the linkage.

 

[rgtrough]

Hey 69, is this a mechanical or vacuum secondary carb?

 

[fine69]

This is a fairly common problem and can be fixed. First, be sure the problem is with the linkage and not with another aspect of the carb.

With engine off, have someone sit in the car and push the gas pedal to the floor while you observe the throttle linkage on the drivers side. When the pedal is to the floor, grab the linkage and see if it is wide open or if it has more travel than the gas pedal allows. If short on pedal travel, there are several possible fixes.

(1) If you used the stock metal throttle linkage bracket that is attached to the rear of the carb, simply adjust the throttle cable. The cable is attached to it via a tubular clamping bracket. Loosen the clamp, slid the cable 1/2 inch or so, retighten the clamp, and check operation of the linkage. (One person in car pushing on accel. pedal, other watching the linkage travel). A very minor adjustment of the cable in the tubular clamping bracket makes a BIG difference and usually solves the problem--especially on Q Jets--but should work on your Edelbrock.

Other possible fixes include (2) bending the metal linkage throttle bracket that is attached to the rear of the carb; or (3) bending the accel. rod under the dash so that you get full movement of the linkage.

George,

Thanks for the info. It seemed to do the trick! I may need to do a further adjustment as it may be idling too fast.

 

[fine69]

Hey 69, is this a mechanical or vacuum secondary carb?

It's a vacuum secondary type... Edelbrock 650 AVS (which stands for "adjustable vacuum secondaries").

 

[JohnZ]

AVS = Air Valve Secondary. The secondary throttle plates are mechanically-operated, but secondary airflow (and fuel metering) is controlled by the large air valve at the top, which is spring-loaded, and its opening rate is determined by airflow through the secondary venturis.