High speed idle not high speed idling.

[AirSpeed]

After I installed a new crate 350 in my truck the high speed idle on my Quadrajet isn't working right. It worked great for several years. I did clean all the years of goo off of it but was careful not to mess up any of the linkage. I cannot see the problem! I've messed around with it, trying to figure out how it operates but it's cold outside and the issue eludes me! It used to hold the throttle open just a little until it warmed up then shut off with a tap of the gas pedal. Anyone have a simple explanation what I should be looking for?

[trac209]

Is the choke closing fully when engine is cold and throttle is pressed to set the choke? If it is then check the fast idle cam to see if it's rising up to set the fast idle. A pic might be of help as well

[AirSpeed]

Originally Posted by trac209

Is the choke closing fully when engine is cold and throttle is pressed to set the choke? If it is then check the fast idle cam to see if it's rising up to set the fast idle. A pic might be of help as well

The choke does close all the way once I press the accelerator all the way down, it starts great but I have to hold the gas peddle till it's warm. I'll have to look closer tomorrow, It's tough for me to work on my truck when's its cold, I have raynauds syndrome in my hands and my fingers turn white and hurt like hell below 50 F. And it's been in the 30s. Trying to get as much info as possible so I can figure it out fast! Thanks!

[R.L.]

That sounds like something in your vacuum somewhere. Are all your hoses hooked up the same? How about your air breather any changes in that? Just a thought and I know you cant tell without taking the intake off but does this new engine have a valley pan?
Hope this helps.

[AirSpeed]

Originally Posted by R.L.

That sounds like something in your vacuum somewhere. Are all your hoses hooked up the same? How about your air breather any changes in that? Just a thought and I know you cant tell without taking the intake off but does this new engine have a valley pan?
Hope this helps.

All the hoses are connected the same. As for a valley pan, no, unless you're talking of the sheet metal riveted to the underside of the intake?

[slikside]

Originally Posted by trac209

Is the choke closing fully when engine is cold and throttle is pressed to set the choke? If it is then check the fast idle cam to see if it's rising up to set the fast idle. A pic might be of help as well

^^This^^


That whole assembly needs to be able to move freely when cold and warm. The fast idle cam is what the throttle assembly should be resting on when you first start it after setting the choke. Sounds like it is not engaging.

[R.L.]

Yes I was talking about the sheet medal under the intake but it sounds like Slickside has probably got it.

[davischevy]

Cold weather fix is, spray the passenger side of the carb with carb cleaner, then soak with spray lube or penetrant.

[mechanicalman]

Originally Posted by AirSpeed

After I installed a new crate 350 in my truck the high speed idle on my Quadrajet isn't working right. It worked great for several years. I did clean all the years of goo off of it but was careful not to mess up any of the linkage. I cannot see the problem! I've messed around with it, trying to figure out how it operates but it's cold outside and the issue eludes me! It used to hold the throttle open just a little until it warmed up then shut off with a tap of the gas pedal. Anyone have a simple explanation what I should be looking for?

A simple explanation would be to say you are likely lean due to less manifold vacuum because of the bigger camshaft. But, that's where "simple" ends because most every choke adjustment requires another adjustment to compensate as there are basically three adjustments and they all affect one another.

Let's start by telling us what choke style do you have.

Is it a round choke housing?

Does it have a metal coil covered by sheet metal bolted to the intake manifold?

Does it have electrical wires going to it?

Does it have a rubber hose on the housing going to a metal tube in the intake manifold?

[AirSpeed]

Originally Posted by mechanicalman

A simple explanation would be to say you are likely lean due to less manifold vacuum because of the bigger camshaft. But, that's where "simple" ends because most every choke adjustment requires another adjustment to compensate as there are basically three adjustments and they all affect one another.

Let's start by telling us what choke style do you have.

Is it a round choke housing?

Does it have a metal coil covered by sheet metal bolted to the intake manifold?

Does it have electrical wires going to it?

Does it have a rubber hose on the housing going to a metal tube in the intake manifold?

Mine has the coil mounted to the intake, no wires, has a vacuum diaphragm mounted to it. I've looked up other quadrajets and mine doesn't have the same shaped cam that I've seen on others, more like levers and linkage, I'll take a pic in a bit.

[AirSpeed]

Here's my carb.

[slikside]

Airspeed,

You DO have the cam. I see it. I will see if I can point it out to you.

On the long diagonal bracket that the choke pull-off diaphragm is mounted to...if you look just above that, you will see the top part of it peeking out just above it. It's triangular shaped and has a hole in it, but you can only see 1/2 of the hole.

On the second pic, it's the piece you see between the same bracket, and the body of the carb. In this pic you are looking down the length of it.

In the first pic, you are looking at it's profile.

[slikside]

And what you have is called a "divorced choke". I think implying that it is separate and apart from your carb, as opposed to an electric one which is well, electric for one, but is mounted integrally with the carb. That's my understanding anyway.

But I have the same divorced choke. When you first press your gas pedal to set the choke for a cold start, of course the choke plate should close, but that fast idle cam (FIC) should be raised to full up. The underside of that FIC is where the action takes place. At this point all that linkage places the choke plate, FIC, and throttle linkage in the proper position for a cold start.

When the motor fires, the primary throttle shaft is held open, at just the right point for a "fast idle" by the FIC. When you tap the gas peddle to "step down" the idle, what you are doing is moving that underside of the FIC to the next "step' down. The front part of that cam that is easiest to see drops down a notch when that happens. I think there are at least 3 "steps" on the FIC.

I used to have a bunch of pic of that stuff when I rebuilt my carb, but must have deleted them after the job was done.

Any how, that's a quick once over of how that set up works. I remember it being an intricate set up, and that's why I took those photos as I was taking it apart.

Oh, there is ANOTHER cam with an arm that should be under the arm of the FIC. That is how the FIC gets raised into position when you set the choke.

[AirSpeed]

Originally Posted by slikside

Airspeed,

You DO have the cam. I see it. I will see if I can point it out to you.

On the long diagonal bracket that the choke pull-off diaphragm is mounted to...if you look just above that, you will see the top part of it peeking out just above it. It's triangular shaped and has a hole in it, but you can only see 1/2 of the hole.

On the second pic, it's the piece you see between the same bracket, and the body of the carb. In this pic you are looking down the length of it.

In the first pic, you are looking at it's profile.

The cams I looked at are more of a round segmented shape with flat spots, I just don't see that on mine. I must have been looking at different model quadrajets.

[AirSpeed]

Originally Posted by slikside

And what you have is called a "divorced choke". I think implying that it is separate and apart from your carb, as opposed to an electric one which is well, electric for one, but is mounted integrally with the carb. That's my understanding anyway.

But I have the same divorced choke. When you first press your gas pedal to set the choke for a cold start, of course the choke plate should close, but that fast idle cam (FIC) should be raised to full up. The underside of that FIC is where the action takes place. At this point all that linkage places the choke plate, FIC, and throttle linkage in the proper position for a cold start.

When the motor fires, the primary throttle shaft is held open, at just the right point for a "fast idle" by the FIC. When you tap the gas peddle to "step down" the idle, what you are doing is moving that underside of the FIC to the next "step' down. The front part of that cam that is easiest to see drops down a notch when that happens. I think there are at least 3 "steps" on the FIC.

I used to have a bunch of pic of that stuff when I rebuilt my carb, but must have deleted them after the job was done.

Any how, that's a quick once over of how that set up works. I remember it being an intricate set up, and that's why I took those photos as I was taking it apart.

Oh, there is ANOTHER cam with an arm that should be under the arm of the FIC. That is how the FIC gets raised into position when you set the choke.

Thanks, I'll check it out this afternoon if it doesn't start snowing!

[slikside]

On close analysis, I can see that all your parts are there, and appear to be hooked up properly. So something is gumming up the works, or something else is responsible for your problem.

I know that those diaphragms do fail. I forget exactly when that comes into play, but it should be able to hold vacuum for a couple minutes or so. If you have a hand vacuum pump, you can test it.

Hopefully you don't spend your whole day dealing with this (unless you really want to!)

Happy Thanksgiving!

[geezer#99]

Since your choke is working like it's supposed to, why not just turn up the high idle screw.
It's in this last pic on page 4.
http://www.vetteprojects.com/kstyer/quadrajet_4.htm

[425HP409]

Geezer has it right, turn the fast idle screw up, it is located at the bottom of the choke mechanism facing forward. You can access it with a long screwdriver. You need to also make sure the the vacuum pot on the carburetor is working properly, it should close when the engine starts. It should also hold a vacuum. It is called a "Choke Pulloff". It has two functions:
1. When the engine first starts it closes by engine vacuum, which opens the choke plate slightly so the engine will not run too rich and flood.
2. It allows the secondary air valve to open slowly on full throttle acceleration to keep the engine from having a "lean out".
If the choke Pulloff is working properly, raise the fast idle by the screw on the bottom of the choke mechanism. This should allow the carburetor to work properly, and the engine to stay running when cold.

[trac209]

on closer inspection there's nothing that should hold the linkage up. A pic of the carb with the choke set on a cold carb could be helpful. If it's not going up on the choke closed setting no amount of turning the fast idle screw will help

[geezer#99]

Ah!!
But it is going up!!
There's evidence of it right there in the pic!!
A tell-tale sign!
Secondary lockout!!

[davischevy]

I wasn't kidding. I shot all the moving parts on mine with spray lube a while back, and it made a world of difference. If it don't help, what have you lost?

[Steeveedee]

Check to see if your carburetor base gasket is the same thickness as the one you took off. A thinner gasket will cause less choke closing, and will present the symptoms you are describing.

[AirSpeed]

Had a few minutes a sun to look at my carb today, I noticed the lever in the photo where my finger is pointing has friction when I move it, it has a lot of drag as I try to move it. I can't see anything rubbing against it and am curious if this friction is supposed to be there? I'd guess I have to give it about a quarter pound of pressure to get it to move. Should that sucker move freely or is it supposed to have drag? Once it moves down a little it starts to move freely.
I also noticed when I disconect the vac line from carb to vac advance on the distributor that there's no vacuum at the carb fitting, should there be vacuum here? It's the vac port on the right front of the quadrajet. It makes no difference whether it's connected or not. Do different ports have different amounts of vacuum? Should some ports have no vacuum? Does the vacuum take place under certain conditions? Here's the lever I was talking about,

[AirSpeed]

Originally Posted by Steeveedee

Check to see if your carburetor base gasket is the same thickness as the one you took off. A thinner gasket will cause less choke closing, and will present the symptoms you are describing.

I actually used the same gasket, it was in good shape.

[mechanicalman]

Originally Posted by AirSpeed

Here's my carb.

Speed-the choke linkage from the coil on the manifold seems to be dragging against the metal housing as depicted in your picture.

Just for grins and giggles, un-snap the sheet metal housing from the base and see if it frees up your choke.