My question is a variation on several others out here, but hopefully I can get some advice or least confirmation that I'm on the right track. I have a 1968 DeVille Convertible, that I've owned since 1986, and has been "in the family" since new. I am 99% sure that the engine, carb, manifold, etc are all original. The car runs well most of the time but my issue is about 5 minutes during warmup. The car starts immediately and runs well. I can kick off the fast idle and choke with a stab of the gas pedal and it continues to idle smoothly. As soon as I try to drive it and touch the gas pedal, the fast idle and choke re-engage, and it starts to load up. I can throw it in neutral, stab the gas pedal and kick off the chock/fast idle only to repeat the cycle until it full warms up. Once hot, it runs great again. I'm guessing from the other threads that the spring in my divorced choke is no longer working right, but finding a replacement spring is next to impossible. They are mostly expensive NOS parts that may not be in any better shape that what I already have. I see an electric replacement is available from Mike's carburetor parts but I'm also seeing mixed reviews on them. I also saw a thread with a link to a spring on quadrajetparts.com suggesting it might work. Any reports of success or failure with this spring? Thanks.
https://quadrajetparts.com/choke-metal-thermostat-spring-1251f-p-1389.html
I would start with an inspection. If you can't see in the well remove it to make sure its clean in there. It is a well so it can collect all sorts of things that could either physically interact with the spring or maybe insulate it so the heat transfer is slower.
If its all clean and looks to be in good working order then I would take a good look at the main throttle shafts and pivots of all the linkages. You may have something warn and flopping around too much so its catching when it shouldn't while you are still in that transitional stage.
If that all looks good then I would grab the manual and check but not yet make any adjustments. If something appears off keep checking the rest of the procedure to see what else may be off and see if you can see any reason for it to be off. You don't want to just start adjusting stuff without knowing how it got off in the first place.
If nothing looks way off then maybe it just needs a little tweak which I think is done with the rod from the spring. From memory I think it pushes up? So unbending it a bit would make it get a little higher a little sooner. IF it pulls then you would want to make the rod shorter. If longer is what needed you can try washers under the spring part, that will give it a bit of a head start but that will also make the well less sealed so it may run a little cooler?
What often causes the issues with these divorced setups is the thickness of the carb base gasket. So many different brands and so many applications it doesn't matter the exact height these systems are the ones that end up suffering.
The electric can work but to do them right its a fair amount of wiring and a new oil pressure switch assuming your car just has a light. If its got a gauge its a T and a new sender.
Is your choke vacuum pull-off working? If not this could be the problem. Mike's Carburetor shows they have the pull-off.
vacuum pull-off (https://www.carburetor-parts.com/quadrajet-carburetor-rebuild-kit-k4105)
If you scroll down a little bit, you will see a link on the left side that says "instructions-electronic", which you can click on and it gives all of the instructions for a full rebuild of the carburetor along with the appropriate adjustments.
Daryl Chesterman
Thank you for the replies and excellent suggestions. I've owned the car for 38 years. This has been kind of an insidious issue over the past 10 years or so. I'd start having problems like this, straighten the choke rod a bit, and it would be fine for a few years. The choke rod indeed pushes up to open the choke, and I have rod about as straight as I can make it. This all led me to suspect that the spring was slowly losing its ability to relax and push open the choke. Just took the car to the body shop this morning to have it painted. They're using it for filler work, so it may be a while before I can actually work on it again, but it was loading up on the 6 minute ride over there, settling down only a few blocks before I arrived. But I have been doing body work myself with a lot of dirt so I will take the spring out and clean everything thoroughly in that well. I believe the vacuum break is working to some extent but replacing the vacuum break for $17 is a no-brainer. Shimming the spring is a great idea. I can wrap some foil around the base to minimize heat loss just to verify the fix. Finally, yes I only have the warning light for oil pressure. Sounds like that might be a last resort. Thanks again.
The assembly is held in the well with 2 bolts so you just need to stick a couple washers under it to raise it. I suppose you could try cutting out a gasket as the spacer because that would then maintain the same gap all the way around so the air flow would remain the same.
Those vacuum dodads did different things over the years and depending on if there was one or two but if it is a pull off that is just forcing the choke like 1/4" open as soon as the engine starts. It doesn't do anything for the rest of the operation.
If you go look at your 75 the oil pressure switch has 3 terminals on it. One tab is still the light which is now named oil/choke. The other two terminals close when there is oil pressure so key on power to one terminal then if there is oil pressure (engine running) the other terminal sends power to the choke coil. They did this so if you had the key on for some reason it would not start unwinding the choke till the engine was running. Probably not the end of the world these days but was a nice feature.
Quick update: I have solved my rich cold running issue. I replaced the vacuum break and thoroughly cleaned all of the linkage with no success. I then started going through the on-car adjustments in the manual, studying how all of the linkage works (or should work.) There is one rod that goes from the spring to the cold idle linkage on the passenger side of the carb. There is a second rod that goes from the cold idle linkage up through the carb to the actual choke butterfly. As I've come to understand it, the first rod controls how long the cold idle (and corresponding choke setting) stays engaged. The second rod adjusts the amount of choke that is applied for a given cold idle position. For the first rod, shortening it causes the spring to pull the fast idle cam down more quickly. For the second rod, lengthen it "pushes" the choke open further for a relative fast idle setting. The first rod was out of spec by about 1/4 inch (too long.) After adjusting it to spec, it ran much better, but still a bit rich for a minute or two about 2 minutes after the cold start. Shortened it up a bit more and it is close to perfect, but I prefer it a little "cold blooded" to prolonged fast idle/rich running.
I am not sure I follow your descriptions, however using the service manual to adjust the linkage and choke settings is a great place to start and will likely clear up most issues with cold start and warmup. Also, using the service manual with a tachometer to correctly set the fast idle will help.
This is how the quadrajet works from a cold start.
1. stab the accelerator pedal once to set the choke. If the engine is cold enough, the choke butterfly should snap shut tightly.
2. Turn the ignition key and start the car.
3. When the engine builds vacuum (should happen within seconds), the vacuum break will push the choke butterfly open slightly (adjusting the linkage according to the manual will greatly help this process). This will allow the engine to get a little air and not blubber from too much fuel.
4. As the car warms up the choke spring should gradually open the choke and eventually will move off of the fast idle position. Adjusting the lever on the choke spring will control how long the choke and fast idle is engaged.
You only get to do those manual adjustments one time per day. To do it right, it has to be an overnight cooling off.