Can't get idle down AFTER re-activating choke:

[fussfeld]

i can't get the idle down to normal in drive since i reactivated the choke. (new quadrajet)


1) i had wired the choke AND fast-idle cam completely open last summer, because i needed the truck running asap and didn't have time to mess with this back then. And it ran great with idle in neutral around 800-900 and in gear 500-600rpm.

2) After reactivating the choke (because it got cold) i can't get the curb idle down to normal---which is 500-600 rpm in drive. Now it's 700-800rpm in gear which isn't bad but it's not optimal.

a) The choke IS opening normally.
b) Hi step, hi mid step are definitely functioning normally. Not sure about low mid step, although the fast idle cam DOES appear to be moving to it's last position each time the choke opens fully.
c) i have the curb idle screw all the way out to the point that the throttle arm is barely touching it, if at all.
d) i did turn the fast idle screw out quite a bit to some improvement, but this shouldn't affect curb idle which makes me think something isn't right here......
Before this idle was about 900 rpm in gear.

Just curious for your general thoughts on this and what i might be looking for? i have not ruled out the possibility of a vacuum leak, but do not feel strongly about it because what are the chances i could have gained a vacuum leak EXACTLY when i reactivated the choke?

i have also not ruled out the possibility of either a sticky vacuum advance or centrifugal advance, but again what are the chances this could have happened at EXACTLY the same time i reactivated the choke?

 

[Georgeb]

If I remember correctly the fast idle cam should drop to the point that the screw does not contact it at all when off choke. Check the linkage to make sure it is operating freely.

 

[74 Shortbed]

If I remember correctly the fast idle cam should drop to the point that the screw does not contact it at all when off choke.

That is correct..

 

[bedwards]

With the idle screw completely backed off, I'd shine a light down the carb and see if the butterflies are completely closed when the choke is off. If this started when you hooked the choke back up, its bound to not be pulling completely off when warm and one of the fast idle steps is catching it.

 

[Georgeb]

Either the fast idle cam is sticking or the choke is not adjusted correctly. If you are using the electric version with the round black cover is the cover fastened with rivets or screws? If screws you can make adjustments to it rather easily. I would mark it for reference and adjust it so that the fast idle cam can just drop out and clear the screw. If you go to far it may not close completely. Now readjust the base idle screw. Lastly enguage the fast idle cam, start the engine and asjust the fast idle to a comfortable idle. I liked 1500 rpm but thats my preference.
After the truck sits overnight check that the choke closes all the way by fully opening the throttle plates. Should only require three full
Pumps to start an engine that was run the night before. I hope
This helps. Good luck!

 

[fussfeld]

Ok, as it turns out, the choke lever and thus fast idle cam WERE NOT going down all the way----it stayed on the very last step of the fast idle cam apparently;

It APPEARED as if they both went down all the way, but upon further inspection they did not. (even though the choke plate itself DID open up all the way)

What i then did, on a whim, was to re-wire the choke lever and fast idle cam all the way down with a ziptie and turn the choke coil fully open, as i had it last summer. And idle returned to normal----900-1000 in neutral and 500-600 in gear.


So, i've identified the problem; The choke plate DOES open fully vertical after about 2 minutes, but the fast idle cam does not go further than the last step.

But i don't know where/how/what to adjust?

 

[fussfeld]

i think i got it:

If we scroll down to the third picture and focus on the top half of that picture:
http://vetteworks.tripod.com/qjet.htm

What i did was to adjust the choke ROD by bending it (making it more straight really) so that the "triangle thing" ( i think the correct term is coil tang---the part that actually contacts the choke coil) would clear if i put a 1/8" drill bit in the hole (yes there is a hole. Or an indentation to insert a drill bit into since the hole technically doesn't go all the way thru)

i THINK what was happening was that the way the rod originally was, it was causing the choke coil to start off "wrong"/too "late". Such that when the choke coil WAS fully relaxed, the way the rod was setup, it didn't allow the fast idle cam to travel past it's final step----because the choke coil could not extend further

It's kinda hard to explain all this (also i did not word things the best), but i think the best way to go about working on carbs in general is to have good books, service manuals etc. AND to have a spare carb off the car where you can see and touch it in 3D as you read the books and manual. i think this helps you understand it much, much better.

Anyways, this procedure has apparently solved the problem.

 

[Georgeb]

Nice job! Yeah, thats how its done.