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Q-Jet and Electric Choke

Bill75

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75 Coupe ZZ4, Brodix IK-180's, Headers,TK0-500
I had to do away with the perfectly working mechanical choke on my Q-Jet when I switched to this ZZ4 motor so I replaced it with an electric one that's never worked worth a darn. I think the housing with the bi-metalic spring I have is made by Edlebrock, it has the number 3182A on the outside.
I've set it up properly but it only wants to open about 1/2 way no matter how long the engine runs. I'm getting 12volts to the unit ok, I wired it to the wiper motor feed and the mechanical linkage appears to be functioning properly, just seems like the bi-metalic spring inside isn't traveling far enough to complete the job.
Is there anything out there that WORKS RELIABLY that someone could recommend?

Thanks
 

Evolution1980

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I had to do away with the perfectly working mechanical choke on my Q-Jet when I switched to this ZZ4 motor...
Why?
 
Joined
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1981 HD Suspension; ZN1 Option
Bill,

Observe the choke plate while you rotate the electric choke cap (of course, loosen the 3 screws first) clockwise and counterclockwise. If the choke plate does not move, then either you have a broken bi-metalic spring or the pin on the cap is not engaging the spring end hole.

Your Vette book should have the rod diameter size for setting the choke plate. The short abbreviated process is as follows:

With the choke cold, and using the correct rod diameter, rotate the choke cap until you can slide the rod in between the choke plate and the horn. Do not drop the rod into the horn!! This is the gap that it should have when it is cold.

Once you set it, snug the choke cap screws, and start the engine. When warm, the choke plate should be vertical or nearly vertical in the horn.
 

Evolution1980

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The heads are not machined for the heat tubes, there's a plate over the opening on our manifold. The Brodix heads I just put on are the same way.
OK, here comes my ignorance of the carbs. I thought we both had the exact same carb (OEM, 1975 & 1980, QJet 750 blah blah blah). I didn't have to make any changes to my carb when I put it on the ZZ4, nor the intake or heads on the engine. So what is different about our setups?
:confused:confused;shrug
 

Bill75

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Messages
698
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Somers CT
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75 Coupe ZZ4, Brodix IK-180's, Headers,TK0-500
OK, here comes my ignorance of the carbs. I thought we both had the exact same carb (OEM, 1975 & 1980, QJet 750 blah blah blah). I didn't have to make any changes to my carb when I put it on the ZZ4, nor the intake or heads on the engine. So what is different about our setups?
:confused:confused;shrug

Here's a picture of my old motor, the arrow points to the choke tube. Under the plate is a loop of steel tubing that goes down thru the intake and into the head. It gets heat back and circulates it thru the chokes bi-metalic spring that operates the choke. Your original 80 motor might be different but your ZZ4 should have a steel plate over that area in the intake manifold. If you remove the plate there's a cutout in the intake but there won't be any place for it in the head.

Choketubelocation.jpg
 

Bill75

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Somers CT
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75 Coupe ZZ4, Brodix IK-180's, Headers,TK0-500
Bill,

Observe the choke plate while you rotate the electric choke cap (of course, loosen the 3 screws first) clockwise and counterclockwise. If the choke plate does not move, then either you have a broken bi-metalic spring or the pin on the cap is not engaging the spring end hole.

Your Vette book should have the rod diameter size for setting the choke plate. The short abbreviated process is as follows:

With the choke cold, and using the correct rod diameter, rotate the choke cap until you can slide the rod in between the choke plate and the horn. Do not drop the rod into the horn!! This is the gap that it should have when it is cold.

Once you set it, snug the choke cap screws, and start the engine. When warm, the choke plate should be vertical or nearly vertical in the horn.

Hi Gerry,

Thanks for the detailed procedure!! I guess I just have the wrong choke plate and bi-metalic spring, it just doesn't have enough travel to open it up all the way. I'll order a new one, I can't find reference to the p/n on the outside of mine anywhere so the guy at the speed shop must have gotten an old "hanger queen" off the shelf. The right one is supposed to be an Edelbrock p/n 1932.
I'll try not to drop the rod. YIKES, don't even think that because I'll do it:eek

Bill
 

Evolution1980

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Here's a picture of my old motor, the arrow points to the choke tube. Under the plate is a loop of steel tubing that goes down thru the intake and into the head. It gets heat back and circulates it thru the chokes bi-metalic spring that operates the choke. Your original 80 motor might be different but your ZZ4 should have a steel plate over that area in the intake manifold. If you remove the plate there's a cutout in the intake but there won't be any place for it in the head.
Ahh yes, it appears I have an electric choke. I have the connection on the choke assm that you have with the tube coming out of it, but looks like mine was plugged many many moons ago. And yeah, I have that cover plate (two plates, actually) on my manifold.
 

Vette79

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1979 L-48 Black Coupe
Gerry, is there a very simple way to adjust the choke that uses the heat tube? When i start my 79 it idles at 1,000 RPM. Does not go higher nor does it drop until I drive it for a few minutes and then it idles around 700 RPM's on the TACH. I am currently as far clockwise as you can go and then I went counter-clockwise two increments. I think I have lost a little bit of HP as well possibly due to the choke binding up. After making adjustments to choke do I need to adjust idle mixture screws?
Maybe I should just go with an electric choke? Difficult to convert?
 
Joined
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1981 HD Suspension; ZN1 Option
... Under the plate is a loop of steel tubing that goes down thru the intake and into the head. It gets heat back and circulates it thru the chokes bi-metalic spring that operates the choke. Your original 80 motor might be different but your ZZ4 should have a steel plate over that area in the intake manifold. If you remove the plate there's a cutout in the intake but there won't be any place for it in the head.

So... this sounds to me like you're not getting any heated signal back to the spring, so your plate won't open all the way, for there is not any heated air signal expanding the spring.

Have you considered switching to an electric-choke? ;shrug With the electric choke, the heating is being done by the electrical current facing resistance on the spring and the spring heating-up.

On the Q-Jet, I am not sure if a divorced-setup is available; however, and just as an illustration only, the Holly can be retrofitted with divorced-style components. I believe that they even have a sensor that when the temperature is reached, the sensor cuts-off the current to the bi-metallic spring.
 

Vette79

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1979 L-48 Black Coupe
All the pieces are in place and I would like to use whats available. I think it just needs adjustment.
 

Bill75

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75 Coupe ZZ4, Brodix IK-180's, Headers,TK0-500
Jeff,

I'm a little embarred to admit this but I discovered that when I put on the plastic cover containing the bimetalic spring I had misaligned it and didn't actually "capture" the mechanism in the carb that's hooked to the choke. The spring was working but it wasen't hooked to the carb correctly so the choke wasen't able to go full open. Don't know if you've had it apart or not but you might want to take a look inside. Just slowly remove the cover so you can see as it comes apart.

Also check to see that the small hole inside the choke housing at the 5:00 position is free and clear. That's a path the vacuum that pulls the heated air thru the tube. If it's plugged the air won't circulate and it'll take forever to heat up.

If you need a picture I can take one later, post if needed.

Bill
 

Vette79

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1979 L-48 Black Coupe
OK. So after work today I went two increments counter-clockwise on the choke prior to starting. The Vette started and remained at 1000 RPM on tach. When temperature reached 165 and vacuum reached 18-19 PSI on vacuum guage I tapped the throttle. RPM's went down to 700-800 RPM's. Took it out for a spin and now I have better response (HP). What needs to be adjusted to have the RPM's increased to warm up the Vette faster? Or should I even continue to adjust?
 

Evolution1980

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Bill75

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Messages
698
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Somers CT
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75 Coupe ZZ4, Brodix IK-180's, Headers,TK0-500
You could adjust the fast idle screw located on the passenger side of the carb. It's down low tucked in under the choke/fast idle linkage. But 1000 rpm is pretty close to where I might leave it.

Bill
 
Joined
Apr 29, 2001
Messages
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Location
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Corvette
1981 HD Suspension; ZN1 Option
Gerry, is there a very simple way to adjust the choke that uses the heat tube? When i start my 79 it idles at 1,000 RPM. Does not go higher nor does it drop until I drive it for a few minutes and then it idles around 700 RPM's on the TACH. I am currently as far clockwise as you can go and then I went counter-clockwise two increments. I think I have lost a little bit of HP as well possibly due to the choke binding up. After making adjustments to choke do I need to adjust idle mixture screws?
Maybe I should just go with an electric choke? Difficult to convert?

Jeff,

Sorry for the late reply.

The only way to adjust how high the fast idle gets is like Bill explained. And the easiest way I know is to use an Lisle carburetor adjustment tool. The one I have has a flexible shank, so it will get around piping or other obstacles. It comes with adapters (sort-of-like a tool socket concept) that adjust fast idle, idle mixture, and even throttle position sensor.

Also remember that the turning of the choke cap adjusts how long the choke will remain "ON" for the spring mechanism to release the choke lock-out. That is why when you kick the accelerator, and the spring has not expanded long enough, then the choke won't come-off and the engine could still remain at the fast idle speed (but there are also other "steps" carved into the lever to allow a somewhat lower rpm in between a cold choke spring and a hot choke spring). :crazy

Anyway, seems like you have a handle on the issue.
 

Vette79

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Jan 23, 2007
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Millersville, MD
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1979 L-48 Black Coupe
Bill and Gerry, thanks for the info. Today before starting I turned the choke cover clockwise two increments putting it at the second increment from center to have a short choke duration. I also adjusted the fast idle screw clockwise to increase the RPM's while choke is operational during cold start. It went to around 1300 RPM's and after about five minutes I hit the throttle and RPM's lowered to around 1000 RPM's. After the Vette was fully warm my idle was at 700-800 RPM's. So, it appears that I am getting the hang of this. Took the Vette out for a spin and everything is great. Is there any reason for me to adjust the idle mixture screws? Another question that I have is "Would there be any benefit to removing the stock dual snorkel air cleaner"?
 

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