Q-jet Rod Style Choke Problem

[pontiacratrod]

i just purchased a rebuilt quadrajet for a '78 sub and installed it on the car. when i go to start it, it revs up real high and then dies. i noticed that the choke is opening all the way almost in unison with the engine starting. the minute i tap the gas pedal it comes off high idle and dies. ive never seen a choke setup like this before so im a little confused. its got linkage and a rod with a spring that goes into the choke pulloff. i dont know how it works, how to adjust it and i dont even know if i can put a manual choke on it. please enlighten me....
bob

 

[Leper]

need more info

Disconnect the throttle cable and see if it changes. Idle, float, and choke settings can cause that. So can an electrical problem. what kind of choke on new/old.? Manual? Electric? heat pipe?

 

[dyeager535]

First things first, good physical inspection...vacuum leaks!

The choke pulloff is supposed to just BARELY crack the choke.

What you want, engine cold after sitting over night, is to hit the pedal once, and the choke to snap shut COMPLETELY. No gap between the choke blade and the carb casting. You do not want there to be excessive tension when it's shut, just enough so that the choke closes fully, every time. You need to be careful here...spring tension (from the choke) only gets you so far...the rod that is connected to the choke plate is what determines how far the choke plate is pushed based on the choke coil. Too short, choke acts very quickly, and may not open far enough. Adjusting the rod should be the last step of setting the choke open/close points.

Once you've got that set, you'll want to set the choke pulloff so that it barely cracks the throttle blade when it sees vacuum.

Choke pulloff ONLY serves to make sure the engine gets enough air to run, after an initially very rich mix. (closed choke)

Fast idle is handled with a screw on the passenger side of the carb. I wouldn't mess with it until I was sure the choke coil tension/rod length is right on the carb. The fast idle is controlled via the choke coil, if it's opening too fast, too little choke coil tension is a likely cause.

Chokes are pretty hard to get right, typically you need to run the engine through a few cycles to get the high idle RPM's right, the opening rate right, etc.

 

[pontiacratrod]

the choke sets fine when i hit the gas pedal. closes all the way and stays shut when its started. the problem is that the choke opens almost imediately so when i go to kick off fast idle, it dies. so then, in order to restart it i have to get out and set the choke by hand. does this sound like the choke just isnt adjusted at all? like i said ive only had manual chokes and the heat stove chokes. this linkage thing doesnt make much sense to me. the carb is a brand new quadrajet reman from holley. you would think that they would just bolt on and go.... must be my dream world kicking in again....

 

[dyeager535]

Unless it's riveted, you loosen the three screws on the choke coil housing, and then adjust tension. However, if it's pulling off immediately, it probably needs both the rod and tension adjusted. If you loosen the choke coil, you'll probably not get the choke plate to snap shut as it should. Again, mess with this with the engine shut, you can "reset" the choke (as you'd find it in the morning, before you kick the throttle) by holding the choke plate open and fiddling with the choke linkage. I can't recall which piece exactly disengages the choke to let you "reset" it cold, but you do have to hold the choke plate open to get it to reset. Once you start it, you are out of luck for hours.

Easy enough to mark the bakelite choke coil portion in relation to the choke coil housing before moving it around, to make sure you can at least go back to where you started from.

If you apply vacuum to the choke pulloff, does it pull the choke open a bit? You can do this on a cold engine, not starting it, after setting the choke. You should get a gap there. No point in trying to fix one portion and ignoring another portion that also isn't working right.