Adjusting the choke (Non-electronic Quadrajet)

[guido666]

I have a 454 with a Quadrajet out of a '77 Cadillac 500 (no electronics). It is my opinion that the choke is way to much engaged. I just rebuilt the engine this summer and it was doing good while it was warm, and now that it's cold, in order to start it I have to crank the engine then hit the gas at the moment I stop cranking. How can I properly adjust the choke so that it will start normally again?

 

[3 on the tree]

Sounds to me like the choke IS NOT working at all. If it is like the ones I am familiar with try this. Pass side of carb, there is a round,black cover bout 1.25 inches in diameter. There should be 3 screws around the edge of it. Loosen up those screws. Use a piece of wire to hold the throttle open just a little bit. Now rotate that black piece till the butterfly closes almost all the way. There should be a SMALL gap between the edge of the butterfly and the side of the carb. Tighten the screws back down. The choke should be set close enough to start now. Try it cold, pump the gas 2 or 3 times, keep foot off gas and hit the starter. It should bust off and run now. Backing up-have you pulled the air cleaner when it is cold to see if the choke is working? After pumping the gas pedal, take the top off the air cleaner and look at the top of the carb to see if the butterfly is closing. I'm betting its not.

 

[guido666]

I completely rebuilt the carb, and you obviously have to take the choke apart to do that. I think I just reset it incorrectly when I installed it again (or it wasn't cold enough out for it to really close fully).

Why do I hold the throttle open a little bit? And why with a wire? Why not just reach over there? I'm not second guessing, it just doesn't seem to make sense what I'm trying to do from your instructions.

So when I adjust the choke until it almost closes, how far of a gap should there be? 1/8"?

 

[mechted]

using a wire for a feeler guage... it should actually be something like 0.07" (???) the last time i did it, i used the truck key, (yes i measured with the caliper first) and it was right about they feeler gauge they wanted me to use

there should be instructions in the rebuilt kit you got about setting the choke, i recommend going through those procedures and seeing how it runs

 

[3 on the tree]

I completely rebuilt the carb, and you obviously have to take the choke apart to do that. I think I just reset it incorrectly when I installed it again (or it wasn't cold enough out for it to really close fully).

Why do I hold the throttle open a little bit? And why with a wire? Why not just reach over there? I'm not second guessing, it just doesn't seem to make sense what I'm trying to do from your instructions.

So when I adjust the choke until it almost closes, how far of a gap should there be? 1/8"?

OK, here goes. The throttle needs to opened just a little bit so the springs that control the fast idle cam can operate. I use a piece of wire to hold the throttle open so I can use both hands to adjust the choke, its just easier for me that way. Good luck, if you can rebuild a Q-Jet, setting the choke up is a piece of cake. How far the choke closes is trial and error, whatever your motor runs best on. I use a paper clip, unfolded so it hangs over. When the butterfly just touches it I call it a good starting point.

 

[dyeager535]

The key to the choke is that if you get it set so that it "snaps shut" to the right spot, you need to make sure that the choke pulloff does its job just right, and once the choke is fully heated, that the coil is pushing the choke plate open completely. If it's not, that means you've got to straighten the linkage that is attached to the chokeplate.

If people are quoting instruction manuals then they are probably right, but if your carb has a choke pulloff, IIRC the choke should shut COMPLETELY when you first tap the gas before starting (cold engine of course) and it is the choke pulloffs job to open it that 1/8" or whatever is called for. I can't remember if all Q-jets have a pulloff or not, I think not.

 

[guido666]

Ok, I took a look at my carb, and it has no fast-idle cam, and what it does have is a vacuum solenoid that pulls on the choke. The solenoid is functional. While cranking it doesn't seem to pull on the choke. But at idle it will pull fully and open the choke. Any ideas?

So pumping the gas does nothing because it is in no way linked to the choke, only the vacuum solenoid and the electric choke coil.

When the car is sitting cold, the choke is fully closed, and has spring tension on it. This is even if the choke is adusted fairly "open" according to the little tick marks on the choke housing. With the solenoid fully depressed, it is open about 1/8".

 

[dyeager535]

You mention electric choke coil, to my recollection the Cadillac carbs were similar to olds in that they were hot air, not electric.

So what's the story here? I don't think electric chokes came about until 1981 or so.

 

[guido666]

It's got an electric choke, vacuum choke advance. It's off a '77 Cadillac 500 (according to the number). When I got the rebuild kit for it the instructions were correct for the carb and showed the electric choke and everything. I'm mostly confident it wasn't converted or anything like that. It's just that the choke is not adjusted correctly.

 

[Tominator II]

I would unhook and plug the vacuum advance junk. Adjust the choke when the motor is dead cold so that it just barely fully closes.Move it back and forth several times til it hits that point. Find the little screw that raises idle speed when the choke is closed and set it for a faster idle during warm up. If you dont have that screw then you are bumming. Make sure you are getting juice to the choke and that the choke coil is operational also. If that doesnt work go to a full manual choke, once you are warmed up it wont matter and they always start quick and you get more control. I hope you can make it work well, I run a Holley doublepumper on my 454 because of all the carbs Ive tried it gives me the most power and performance but I have a Caddy Qjet like yours that I might try sometime. I have completely switched choke setups on several different Qjets, it is do-able, its really fun getting the choke rod in the carb to line up with the little linkage arm to the choke butterfly but ive done it with carbs still on the motor and had some good results. Try and get the choke parts from a mid 70s Chevy Qjet. Happy Tweaking!

 

[dyeager535]

Well, if it is electric (and I'm sure you know what you've got!) then there is always the possibility that the circuitry in the choke cover is bad. I didn't even know those did go bad, but I've since seen it. They are insanely expensive to replace. ($70 or so IIRC)

Anyways, not to start anything, if the factory put it there, it's probably best to make it work as designed, unless you completely convert to another choke style. If it was good enough to work on GM's top of the line car model, it probably worked ok. As much as I dislike chokes, I can't complain about any of the ones I've worked with, all were smooth and consistent. Now, others have all sorts of problems and that is frustrating to sit through, as you know.

I'd like some comment on how others have their choke pulloffs set. I'm certain mine snapped shut with a cold engine, but once the engine developed enough vacuum, it quickly pulled the choke open that 1/8" or so. If the pulloff has a leak (rubber diaphram) that might also be an issue. Make sure it holds vacuum, that's always a good preventive maintenance check on those carbs.