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I have a 1970 Corvette with 350hp/350. When operating the throttle I am not getting the full movement on the Quadrajet and thus the secondaries are not opening up. It is probably the original cable, etc. What could be the issue? The pedal feels ok and the carb is idling ok, how could the cable not allow the full movement? It seems odd....if it was the cable too long then a shorter cable would not allow the correct idle?
A picture of the cable bracket located on the rear of the carburetor would help along with a picture of which hole in the carburetor throttle the ball stud is located.
The gas pedal itself is another possibility.
Is there slack in the cable at idle? Disconnect the cable, and check for full movement. Also check the cable retainer on your intake manifold, did it slip?, is it bent. Was it working fine at one time? The geometry to me is very important, in fact I redrilled a new hole in the carb linkage on my q-jet. I wanted more pedal travel at small throttle openings and less travel at wot.
I had the same problem,
Checked everything and all was in order.
Ultimately I decided that years of flooring the gas pedal led to deforming the rod the gas pedal attaches to.
First I studied the pedal linkage shown in the AIM to understand its action.
The fix for me was to simply reach down behind the pedal and pull up on it in small increments to bend the lower portion of the rod upward giving the pedal more travel while checking the carb linkage for full open position.
I had the same problem,
Checked everything and all was in order.
Ultimately I decided that years of flooring the gas pedal led to deforming the rod the gas pedal attaches to.
First I studied the pedal linkage shown in the AIM to understand its action.
The fix for me was to simply reach down behind the pedal and pull up on it in small increments to bend the lower portion of the rod upward giving the pedal more travel while checking the carb linkage for full open position.
That did the trick.
If the linkage has a plastic mount that holds it to the inner firewall, be careful that you do not crack the plastic mount while re-bending the rod.
Another culprit around the pedal could be the "pinch joint" between the pedal bracket and the pivot rod.
The rod and bracket have a D-shaped fit which is clamped down by the bolt and nut shown below.
If that joint is loose, the pedal will have some free-play to the bracket arm.
This happened to me, as I was not getting to WOT even with a pedal mashed to the floor.
Without WOT, my Holley secondaries were never opening, and I was getting maybe ~80% throttle and only sucking off the primaries.
Easy fix to tighten up this nut/bolt (along with "bend" tweak of the arm that was suggested above), and the cable was now starting to actuate the throttle as soon as the pedal was touched.
One way to check the root cause, is to have someone depress the pedal fully to the floor and hold it there (no mats / engine off!), and another person at the carb. Once the pedal is fully depressed, check the throttle linkage. If you still have some additional throw in the throttle travel, then you know there is some "loss" in the cable and/or pedal.
Good luck!
Ask Lars for the latest copy of his "Q-Jet Tuning Paper". Scroll to almost the end and look for the section labeled "Technical Explanation: Help! My Secondaries Don’t Work!". Scroll down to "Issue #3". I did a, c, & d on my stock '73 L82 and it fixed the problem of the secondarys not opening fully. I kept the rubber floor mat (not in the way), but re-oriented the carpet which was preventing the pedal from going to the floor. I removed the gas pedal and bent the steel linkage rod in a vise as I did not want to chance breaking the plastic bracket. I verified all the work by pressing the gas pedal to the floor and watching the secondary throttle open to the wide open position. Took it for a ride and noticed it had more zip. Carb was rebuilt by Lars in 2016 and I have it tuned per his paper. It has been running perfectly and fast.
Mr. Jenkins,
Good info here from the replies. I'll add one more possibility based on the same engine in my 69. If you or any previous owner has changed the factory cast iron intake to the edelbrock performer. The carb sits slightly back toward the firewall with performer causing slack in the cable.
Kind regards,
Norm
12-16-2020, 05:16 PM
only partial throttle
