1974 350 auto vette. How do I know if my secondaries are opening? My understanding is that they do so gradually and only under load, i.e. I cannot test with car in park. Any ideas?

 

First thing would be to actually check if the secondary air intake plate is sticking. This can happen if you over torque the top housing screws, warping things a bit. A little filing with a shop vac sucking will take care of it. The choke needs to be totally warmed up, and pull on the thottle while observing the secondary air plates. If nothing, push the air plate in and watch if the secondary throttle plates are opening, as could be a choke lock out problem. Check power piston movement while at it. Some guy's just give up, and change over to a simpler aftermarket carb. They're usually just looking at disappearing tail lights of well set up Q-Jet cars though. No other carb design even comes close for the street.

 

Thanks for that. The choke is long gone. I live in the tropics. Temp never below 80 here so no issue. But does not having the choke affect the secondaries?

 

The Q-J came w/ a secondary lockout lever closed by choke on pass side. Take a look at pass. side & operate throttle.
Running- if you pull back hard on the throttle momentarily you can see & hear the valve start to open when set up for high power.

 

quadrajets has a very distinctive note when the decondries open, if your car has a relatively quite exhaust you'll diffenetly hear them, also you should notice a power difference in the pull.

 

Take a piece of wire or string and engage the secondary lockout lever so that it won't allow the secondaries to open at WOT. (Wire the secondaries shut.)

Take it for a ride and punch it. If the power is significantly lower as your RPM's climb, then your secondaries were opening under normal conditions.

 

There are a number of "issues" to consider here. You are asking about the air valve opening. The air valve will naturally open under the force of incoming air pressure IF it has no restriction from doing so (due to choke linkage and/or dashpot connected to it) and if the [lower] secondary throttle plates are actually opening.

As mentioned above, for the throttle plates to open, the secondary lockout lever (little "L" shaped arm on pivot just in front of secondary throttle plates on right side) must be freed by the choke mechanism so that it does not prevent those throttle plates from opening.

In addition, the secondary throttle plates will only open IF the accelerator pedal/linkage and the throttle cable are adjusted so that they fully pull the carb linkage when your foot is to the floor. This is actually the first thing to check; and to do so, you need someone else in the car depressing the pedal to the floor while you are under the hood, 1) manually releasing the secondary lockout, 2) holding the secondary air valve open, and 3) looking down into the secondary barrels to see if the lower throttle plates are really opening up completely (plates at exactly vertical). If you can satisfy this pedal/cable/linkage test, then you can validate that the choke will release the lockout arm and that there are not other mechanical restrictions from the air valve opening at WOT.

{Note: The lockout arm is only there so that the engine is not asked for WOT when it is cold. If you want to make certain that this lever doesn't prevent secondary opening, you can remove it from the carb system. You can just loosen the choke linkage mounting screw barely enough to wiggle that are out. But, if you unscrew too much, the choke shaft will disengage with the choke plate arm (inside the carb) and you will have big problems putting it all back together. You make this call.}

Good luck with your "research", andI hope you get it all working well!

 

with 7T1Vette

I would add when manually checking your secondaries, check the lockout by trying it with and without holding the choke open.

 

{?? Counting to 10 ??}