Hi All,
Is there a way that I can tell if the secondaries on my quadrajet are working correctly? I've got a original 350 engine with the Qjet 4MC (number 17056259), when I'm on the open road and punch it, seems like I don't feel the secondaries kick in, very sluggish.
When in idle and parked, I can feel the vacuum holding the secondaries closed, but would like to know if they function correctly somehow. I can manually increase the throttle, but don't see any movement as the power is applied.

many thanks!
james

 

First of all, those aren't the secondary throttle valves you see when you look at the carb. Those are the secondary air valves, which only open in response to engine load. The secondary throttle plates are at the bottom of the carb and are mechanically operated.




You won't see the air valves open if you are revving the engine in PARK. There must be a question about this every month or so. As for your on-road experience, there are a LOT of potential causes for loss of power. If it REALLY is due to the secondaries not opening correctly, depending on the year, the choke will either lock out the air valves or lock out the secondary throttle blades. You need to know which system is on your carb and be sure it's adjusted properly.

The lockout on the throttle blades looks like this:





The lockout on the air valves looks like this:






Here's a pretty good thread on the subject.

 

How much tension is there on your secondary air flaps ? There is an adjustment for that . Check to be sure all your linkages are working and your choke plate is open when the engine is warm .

 

I had a 79 Cadillac years ago that like to have driven me crazy until I learned how to adjust those secondary air flaps or whatever they are called. That was before the internet and websites like this. I don't remember how I learned how to adjust them and don't remember how either. Once I adjusted them the car ran great.

 

Quadrajet Power says - We set them about 3/4 turn from first touch.

 

Besides the lockout issue, it's also good to have someone sit in the car with the engine off and floor the gas pedal. Open the secondary air valves (flappers) and look down the venture and see if the secondary throttle shafts are fully open. If the throttles aren't open fully a linkage adjustment or obstruction (carpet) may be limiting travel.

 

As said, something mechanical could be stopping the secondaries from operating. I had the base plate gasket be a hair off and hold the secondaries from opening. My 70 is also acting this way. I have a 1" open spacer, more gaskets equal more fun.

 

Thank you all for the excellent information, and my apologies for re-hashing old threads.

james