To separate the idle cam from the choke
Wouldn't it be simpler to just run a manual choke? That way you can adjust the choke and idle speed where you need it.
Not if I want control over the idle speed only.
What if the car is all warmed up and yet I want the idle to be a little higher or even lower temporarily?
Much rather have a dial to increase or decrease just the idle without involving the choke.
If also installed with a manual throttle.
Totally sympathetic with that issue.
Here's what I've learned about how an automatic choke is supposed to work. You'll have to investigate whether either of the carbs you've got has all the features.
Initial Choke position: This is where the plate sits when the engine off. Its the maximum restriction to the carb entry.
Qualified Choke position: Plate position immediately upon starting.
* It's opened by manifold vacuum.
* The amount it opens is usually adjusted by increasing or decreasing the spring force on a vacuum diaphram.
* Usually the linkage is such that the qualified position is based on the initial position, not independent.
* It does not effect the throttle fast idle position.
Fast idle cam has two or three steps. In warmer weather the cam's linkage to the choke should rotate it off the upper step(s) pretty quick.
* There may be a way to have the choke 80% open and still have the cam rotated so the throttle is on the second step.
Some carbs have internal vacuum source connection to the choke. They may or may not have a means of adjustment if its internally connected. Some carbs don't have any vacuum source. I think the only solution for them is set the choke for the running position and use pump shot from working the throttle to get it rich enough to fire off.
My own preference is for the choke bimetal to be getting heat from the intake since the intake's temperature is what matters. But that's too complicated for aftermarket carbs so that's not a realistic choice in most cases.
One carb I may use (The Holley Avenger) has the bimetal electric heated style and also a vacuum activated choke pulloff.
If I were to do it with this carb it would be really easy since the idle cam is not physically connected to the choke butterfly.
The cam is lifted by an L in the choke plate linkage rod that goes under the cam and lifts it.
If I did it with this carb and my dial inside the car was backed off to it's lowest setting the entire carb choke and high idle linkage would work exactly as designed by the OEM.
On the 750 Edelbrock electric bi metal the choke and high idle cam are physically connected with a rod, so I would have to separate them by removing that rod or the choke would close some when the idle speed was increased.
And it would always be separate from the choke and not work as designed if I didn't use the manual high idle knob.
This one I would have to use the manual high idle every time I start the car instead of it working normally if I didn't use the manual device.
That's one point in favor of the Holley, but I'm not going to use it just because of this.
I'll decide which carb I like best and then make the mods needed.
