With a little help, I finally got the Vette (a 79, all stock) finished enough to drive for the summer sunday night. I rebuilt the carb myself about a month ago, but never got a chance to start it until Sunday.

First fire-up was fine. No problems. We just wanted to hear it run for a second (and make sure it would start). A short while later, we restarted and the idle was running high, so looking around for the idle adjustment screw ( #1: is it on the driver side or passenger side of the carb?) we screwed something up. When we started it again, the engine revved way up to about redline real fast, so my helper shut it off as soon as he could. After some looking and testing and such, we determined that the secondaries were slightly open which caused the engine to rev way up. We did something, I don't remember what, and it seemed to start up and run fine, so we quit for the night.

After work Monday, I was hoping to take it for a drive around the block, but when I went to start it, the engine revved way up again, and sure enough, the secondaries were partly open. I had another friend come over and we stared at it for a while and found that I didn't have the secondary lockout lever oriented correctly. We fixed that, locked out the secondaries, and the car started fine. So we went on to try to figure out how the secondaries actually open.

According to Lars' paper, they don't open until the car hits higher rpms. We played around and slowly brought the rpm's up in neutral, but the secondaries would not open. The lockout lever would come lose, letting the secondaries free to open, but no such thing. If the rpms were brought up fast, the lockout lever come lose and stay lose and as the rpms started to come down rather fast, the secondaries would no longer be locked out and the rpms would stay up. I'm confused as to how this worked before. In searching the archives, I read that the secondaries will not open unless under a load, not in neutral (#2: is this true?).

A long post, but I like to be thorough. Thanks in advance.

 

The secondary throttle shaft on the Q-Jet is purely mechanical. If the lockout lever is retracted, the secondary throttle will open when the lever is wide open. The airvalve on top will not open unless you have enough airflow to get it to open - you can't "wing" it in neutral and get the airvalve to open. If the lockout is retracted and you have enough throttle cable travel to open the throttle fully, the secondaries are working. However, if the secondary throttle is sticking in the open position, you have a problem that you need to correct.

 

The secondary throttle plates (at the base of the carb) open mechanically as the throttle is opened. The secondary air valve (butterfly on top of carb) is opened by vacuum as the engine demands more cfm. It is possible to assemble the comlex mechanisms of the carb wrong and still get it to go together. It sounds like that may have happened. Study a good exploded diagram of your carb and be sure all the pieces are oriented correctly. The idle adjustment is on the driver's side. The screw on the passenger side is the fast idle adjustment, part of the complex choke mechanism. Good luck and God bless, Sensei

 

Basically then, how I have it now is right, which is kind of what I thought. The secondaries, upon start up, should always be locked out. Only when I'm on the road and I "floor it" will the secondaries unlock and begin to open.

I was just confused and concerned as to why when I punched the accelerator while it was sitting in neutral that the secondaries came unlocked and stayed open. Maybe there's some sort of adjustment to make here?

 

When I say secondaries, I mean the secondary throttle plates, not the secondary air valves.

 

I just read Lars post again for the 5th time....

You're saying that the secondary lockout lever will lockout the secondaries at all times? When mine is retracted and hanging lose, the secondaries are partly cracked open. The spring that puts tension on the throttle plates on the driver side of the car: when its in its "neutral" position, meaning the spring is attached and the secondaries are not locked out, the secondaries are open slightly.

When we locked em out with the lever and slowly brought the rpms up, the lever came lose (allowing the secondaries to come open), yet the secondaries never opened. Which brings me back to answer one of my own quetions that the secondaries only open when the vehicle is in gear and moving.

Hmmmm....Seems so simple, yet that much more confusing.

 

No, the lockout lever should only engage when the choke is closed. If the choke is open, the lever should not be engaged with the throttle shaft pin.

The secondary throttle plates should never be cracked open at all until the progressive linkage pulls them open at about 1/2 primary throttle plate opening.

 

I'm still having a problem I don't know how to fix. I understand what Lars is trying to say: when the car is warmed up, the choke disengages the secondary lockout lever so that when the throttle is mashed, the secondary throttle plates can be opened.

This, however, is my problem. If the carb is sitting there by itself, everything hooked up as it should (or so I think) and the secondary lockout lever is disengaged manually (by hand), the secondary throttle plates crack open due to spring tension. The spring I refer to is the outer one on the driver side of the carb that mounts to the secondary throttle plate shaft. There are 2 on the secondary throttle shaft, a smaller one closest to the carb, and the larger one (the one I'm talking about) furthest from the carb.

It seems to me that the "neutral" position of the throttle plates, when the lockout lever is disengaged, should close the throttle plates. When I relieve the tension on the spring, the throttle plates have a free range of motion from closed to slightly open.

What I just don't understand is why this wasn't a problem before I rebuilt the carb. Maybe I did something wrong, but I can't figure it out. If anyone knows what I'm talking about, how can I fix this?

I'd post pics for clarification, but I don't have a digital camera and my only internet connection is at work on a Unix station

 

Did you remove the secondary throttle shaft springs during your rebuild...? These are not normally removed. The springs, if installed correctly, should hold the secondary throttle shaft very firmly closed. If the springs are making the secondary throttle crack open, you have the springs assembled wrong.

 

the inner spring on the throttle secondary throttle shaft should keep spring pressure on the valves to stay closed unless the link from the primary is opening them. the outer spring could cause a problem if it is bent or twisted, both springs are still avalible new or from a core. the secondary throttle valve should have spring pressure keeping it closed if not that may be the problem, also if there is any warpage of the base, intake manifold, a bent secondary throttle shaft the shaft could stick. when the carb is bolted to the manifold the secondary shaft should still close with the same spring pressure as it did when off the car. If someone bushed the secondary throttle shaft and the secondary throttle only hangs up when the engine is running there could be a bushing fit problem. good luck