QJet Choke and Fast Idle Questions

[Rolled]

Having some issues with a rebuilt quadrajet I purchased from Holey.

Backround -

82 K20
M code heavy emission
hot air choke
350
465
everything is hooked up correctly and nothing is missing under the hood. I just put a crate motor in and made sure everything was installed back to stock so I can pass emissions.


Here is the problem I am having -

The choke just does not seem to opperate correctly. It always wants to go to fast idle even if the motor is at opperating temperature. If I play with the throttle I can get the fast idle cam to fall into the correct position but it just does not want to stay there.

It looks as though gravity is suppose to drop the fast idle cam when the choke coil expands but the linkage is pretty ballanced so there is nothing forcing it down...

I am assuming the spring tension of the choke coil is suppose to force the choke closed when cold. That is how I have it set up. That works just fine but when it heats up, nothing is forcing it open. The coil just backs off and gravity is suppose to make it open?????


If I am wrong and the coil is suppose to force it open when hot (which I prefer) then there is nothing to close it when cold. nothing at all since the fast idle cam and butterfly valve would have to fight gravity all on their own to close up???? So I doubt that is correct...

Either way, how the hell is this hot air choke and fast idle cam suppose to work and how does one set it up?

I have a book and the carb came with manuals and I even have directions from a rebuild kit but none of them reall explain how this thing works. If I set it up like I think the books tell me to, there is nothing to controll the opening of the choke other than gravity so I must be doing something wrong


Tips, advise, tech article, hand holding , any help will be appreciated.

 

[makovai]

i have 1 word for you Edelbrock.
I bought 4 holley 600s and had a holley gooroo come over and he rebuilt 3 of them and none would stay tuned for more than a day. I had this guy bout ready to commit suicide over these carbs.
I bought a brand new 1406 edelbrock and adjusted the idle and haven't touched it for 3 months now.


Note: i din't really want 4 of them, its just when the original was acting up i ran an ad for a replacement and i started trading goodies for them and somehow ended up with 4.

 

[Rolled]

I wish I could use an aftermarket. But I can't. I have to pass emissions and I must have original equiptment on this rig. if not for that, I wold swap it to TBI.

The carb was a Holley reman but it is a Rochester Quadrajet...

 

[pauly383]

You adjust the choke coil so the flap door over the primaries is open a little ( your tune up specs in your manual ) . The weight thingy will drop when choke heats up AND you blip the throttle to release it ( remember you blip throttle once upon entering truck to set the choke ) .

 

[bigblock72]

Is your choke spring on the intake with a rod or is it a round housing on the side of the carb?. If I know what style of choke you have I can get you pointed in the right direction.

 

[Rolled]

You adjust the choke coil so the flap door over the primaries is open a little ( your tune up specs in your manual ) . The weight thingy will drop when choke heats up AND you blip the throttle to release it ( remember you blip throttle once upon entering truck to set the choke ) .

Thats the way it looks but it fails to fall when heated. If I agressively fook with the throttle several times it will slowly work its way down... The weight moves freely with no binding at all. it just does not want to go down. Sometimes when driving, it manages to up a bit from bumps in the road...

It, quite often, goes to the second step on the cam. It is set at 700 rpm and 1900 rpm fast idle. And I believe there is a second step on the fast idle cam that runs at 1450rpm. The motor really likes hanging out there...


I took out the fast idle screw and forced the choke wide open. It runs good but don't know what it will be like on cold mornings. I also have an appointment with the emission inspector today. I hope they do not notice the fast idle screw and choke... I was certain the Jiffy Lube emision inspector would not notice but they failed me for having a new motor. New motors here have to be inspected by a special station. I hope these fellas do not notice what I did to the choke...



Is there any way to adjust the weight so it falls and stays down? I noticed a lot of linkage around it. Maybe some of that controlls the weight...

 

[bigblock72]

The bi-metal spring controls the position of the fast idle cam and the choke butterfly as well. Your problem is related to the choke bi-metal spring not getting hot enough to open the choke all the way and drop the fast idle cam down. If you can describe what style of choke you have I can help you fix it correctly.

 

[pauly383]

try to lube the linkage , you may have overtightened the carb too , putting pressure on it .

 

[Rolled]

Is your choke spring on the intake with a rod or is it a round housing on the side of the carb?. If I know what style of choke you have I can get you pointed in the right direction.

Its a hot air choke not the style that has a choke spring in the manifold. A tube passes through the intake into the exhaust. Inside this tube air circulates to the choke housing. The hot air expands the choke spring.


The bi-metal spring controls the position of the fast idle cam and the choke butterfly as well. Your problem is related to the choke bi-metal spring not getting hot enough to open the choke all the way and drop the fast idle cam down. If you can describe what style of choke you have I can help you fix it correctly.

From what I can tell, the choke spring/coil expands and relieves pressure from the fast idle cam and butterfly valve. After it gets hot enough to do that, it is up to the weight to drop which allows the valve to open all the way and the fast idle cam to drop out. When its cold it does exactly what it is suppose to. the spring pressure forces it closed and if you hit the gas, the fast idle cam is activated.

The choke seems to be operating just fine and allowing plenty of room for this to happen. Its just that the weight does not want to go anywhere on its own. Its not binding, its pretty loose and moves freely. It just likes staying at the top or the middle. Sometimes it bounces back up to the middle. there is nothing forcing it down except gravity which is not enough.

I'm thinking of messing with the weight a bit to see if I can influence it to stay down.

pauly - I'll look into overtightening and try lubing it up.


Thanks for the help guys. Hopefully I'll get this solved and put it behind me... I'm about ready to buy a 1973/1974 Ksomething and swap out the drive train. there is no visual inspections for rigs older than 1975. This way I can do whatever i want under the hood and scrap a carb all together

 

[bigblock72]

If it has tubes going into the manifold then the choke spring is in the housing on the side of the carb. The exhaust crossover may be restricted down to a point where the choke spring isn't getting hot enough to open fully. Try getting an electric choke for it and your problem should be solved. It's an easy swap, just remove or drill fasteners from choke cover (should be three screws or rivets) and replace with an electric one. They are around $40.00, and try getting one for a 85-86 car or truck with a 350, it will bolt on once you cut the little alignment nubby off. Between the exhaust heat and the electric heater your choke should work good.

 

[dyeager535]

Don't forget, if the choke linkage isn't "long" enough, you'll end up tightening the coil to the point that it won't expand far enough to disengage the idle cam. Buddy could never get his right either (One of the Edelbrock Q-jets though) it was either choke on all the time, or off all the time. I'm sure now that it was the length of the choke rod.

 

[Rolled]

I tore it apart, soldered a small nut on the weight, lubed everything up.

It is working correctly now

I think the real problem was either the bolt holding the choke housing on or the screw to the linkage in thechoke housing being to tight.

If I overtightened either of those, the linkage would bind. I have a feeling one of them was just a hair to tight and kept the weight from its freefall.