33 year old choke

Bonnewagon · Dec 4, 2013

So as soon as it is getting serious cold, my choke is acting up. I know it's the cold motor/fast idle function, but it looks fine. When I retract the throttle and set the choke it looks like it does what it should yet the fast idle is not engaging at all. It stays at the hot idle position. So it's a 33 year old all original '80 Q-Jet w/electric choke that I pirated off my Daughter's '80 TA 301. It has been played with some but the choke is original- when's the last time you saw rivets? The secondary pull off I yanked off years ago. I wanted to fix it without removing it from the motor so tried carb cleaner on the linkage first. Nice and clean- no change. Next I drilled out the rivets and found- nothing wrong. I cleaned the coil housing and replaced the rivets with stainless steel screws. At least I can adjust the electric coil now and that does nothing either. Looks like I will be removing the carb for a good eyeballing since I cannot get at the fast idle linkage with it mounted. Rats!

olds307 and 403 · Dec 4, 2013

Have you adjusted the screw for fast idle speed? I can see the one part that comes up with fast idle, there is a second part also. Surprised that choke coil works with the rust.

Bonnewagon · Dec 4, 2013

Yes, I did, and that's even weirder. It's either racing at 2000 rpm, or 550 idle- no in between. I know I had to replace the fast idle screw with a slightly longer one years ago, still don't know why the old one was not catching. Maybe that's a clue.

techg8 · Dec 4, 2013

the choke idle screw was also my first thought.

The cold coil lifts the green arm which lifts the fast idle/choke cam into position and pulls the choke flap closed. From the pics it looks like its working.

If the choke idle screw is set too far out, it will not be able to engage the fast idle cam step and give you the cold start fast idle.

This can also occur if the curb idle screw is set too far in...

Think of a scenario where you take a smaller engine's carb and put it on a larger engine. the carb needs more throttle angle at idle due to CID, cam, idle circuit malfunction, or whatever. So the curb (hot) idle screw is turned in some more.

Now the fast idle screw needs to be longer because it has been rotated further away from the fast idle cam.

EDIT: for the big rpm drop - at a cold start you are probably getting good fast idle cam action, giving you 2000 rpm. When the engine is running the primary pulloff draws in and pulls the green choke arm with it. If the pulloff pulls it too far in, OR again if the screws arent quite right, the fast idle cam will be released to drop too far or the fast idle screw will no longer engage it.

I would go back to the right length fast idle screw and have a look.

I think the interplay of the two idle rpm screws could be your cause?

Bonnewagon · Dec 4, 2013

Could be Ken. Another thing, the weight that gets pushed all the way up by the coil spring, and then presses down as the coil warms up, doesn't seem to be getting all the way up. And when it looks like it is, still nothing.

axisg · Dec 5, 2013

I have this site bookmarked for my own reference. It was helpful when I swapped the qjet back on my car. For your car I would check the choke tension and the choke pull off. It sounds to me as if your choke is not set tight enough to fully engage the fast idle cam ( although in the pics its fully upright and engaged ) and with a weak setting it will not hold the choke for as long as may be needed allowing the choke pull off to pull it off fast idle too soon. Is the primary choke pull off working smoothly ?

http://www.florida4x4.com/tech/quadrajet/index.php

Bonnewagon · Dec 5, 2013

I think my problem is either that the cam is not getting to the fast idle position, or the screw is not meeting the cam. I can force the weight up, drop the throttle, start the motor, and it races to 2000 rpm or whatever I set it at. The pull-off works, and the choke flap opens normally and kicks down just as it should. It looks to be working just like in this GIF.Then I let it get cold and -nothing. I simply have to get it off the motor for a look-see. As winter closes in!

tc1959 · Dec 5, 2013

I was having problems with my original tube heated choke coil on my 78 El Camino so I switched out the Choke coil with a electric one.
AIRTEX / WELLS Part # 2C1032 www.rockauto has it for $13 it is listed for a 79 Cadillac Deville with a 425.
It solved my problem. It starts with one squirt of the accelerator now .

Bonnewagon · Dec 6, 2013

TC, I'm with you there- I convert ALL my Q-jets to electric. I've even stopped using the '60's versions because I can't figure out how to adapt the divorced choke to electric. Now I concentrate on the '75-'80 versions, as the APT is a great tuning tool. Too bad it's raining cats and dogs right now or I'd be yanking that carb off as we speak.

olds307 and 403 · Dec 6, 2013

I wonder if the middle normal step for fast idle speed is worn on the linkage. That arm is moving as it should. I have actually bent the linkage, pretty sure it acted like that. I too always convert hot air chokes to electric.

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33 year old choke

Bonnewagon

Lost in the Labyrinth

olds307 and 403

Geezer

Bonnewagon

Lost in the Labyrinth

techg8

Master Mechanic

Bonnewagon

Lost in the Labyrinth

axisg

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Bonnewagon

Lost in the Labyrinth

tc1959

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Bonnewagon

Lost in the Labyrinth

olds307 and 403

Geezer

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