Hey all,

My 600 & 750 both have Electric choke. I notice that each has a small port on the choke canister that has active vacuum. If you put your finger over this, it changes the idle. This tells me that it is a "leak" unless anyone can help me clarify. The picture attached is not me carb, but it does show the port I am talking about.

The question I have is, should this be plugged or left open? I never see any reference to it on any Edelbrock installation instructions.... Thank you!

Pretty sure you want to leave that open to draw ambient temperature air across the heater coil so the choke stays on more cold, less when hot.

look here

Edelbrock Instructions

Not sure what carb that is, other than not an Edelbrock one.

In this article https://www.hotrodhotline.com/conte...barrel-jim-clark-hot-rod-md#.X68zjhZ7mM8

It states "Vacuum from beneath the venturi in the carburetor has drawn the piston down in the choke housing keeping the choke butterfly open once the engine has reached operating temperature."

Doesn't sound like it should be a vacuum leak. If I remember I;ll look at my carb tomorrow and see if it's open or sealed.

Try a temporary type plug and see what happens. If it doesn't work then unplug them.

That's supposed to draw warm air into the choke housing to help speed warm up. Some people used to attach 1/4 copper tubing to it and wrap it around a header tube back in the day. Some even used to sell a kit that clamped to a header tube with a couple of hose clamps. Some gm app.'s connect that to an EGR port.

Not supposed to draw warm air at all.

Go read the Edelbrock instructions.

This is the general design layout I'm familiar with. Back in the day speeding up choke operation was a emission driven intent. Adding electric speed this process up.

There are three types of automatic chokes.

Exhaust heated, which is what you are familiar with. These tend to carbon up over time and stop working.

Electrically heated, which is what the Edelbrock choke is. This uses an electrical heater, only, to open the choke. Sort of insensitive to engine temperature.

Electrically assisted, which is both. This is similar to what later Mopars used to hurry up opening of the choke for emissions purposes. Mopar used a temperature sensitive resistor to control current thru the heater assist element to make it more sensitive to engine temps.

I have seen Holley's that have a screened washer in that port when they are open to atmosphere. However to the original post yes there will be manifold vacuum there. For the kickpiston to work it needs to flow through...see pict.

The vacuum applied to the piston is calibrated to open the choke valve slightly after engine start to prevent an over rich condition. Necessary for start, but not for idling. The spring that heats up or the electric coil that heats up at a set rate open the choke fully at the calibrated time based on engine being fully warmed up. This allowed a car to function properly in cold weather and be driven immediately after start up, while progressively opening the choke valve and changing mixture quality to meet conditions as engine heated up.

For divorced choke carbs the vacuum pull off canister does the same thing as the Choke piston. Other early carter AFBs had a piston integrated into the top to pull off the choke valve via vacuum.

Normally the inlet receives air from the air cleaner through the exhaust manifold to properly determine engine temperature. For electric you could allow air flow from air cleaner since hot air not needed. Or you could plug it. All depends on if that was original housing or an added electric to a thermal housing. Typically there is a metering orifice in the carb body where the choke housing attaches to the carb body. This meters that air leak into the carb which is typically below the throttle blades and an unmixed air inlet. I believe newer electric chokes from EB do not have that air inlet.

Remember older carter AFBs had vent holes to outside air above the throttle blades for venting purpose. They were a calibrated air leak that did not mix fuel via the venturis.

The vacuum at the open port is from the piston which is not 100% sealed to its bore, the piston pulls the choke blade open and the residual vacuum pulls in fresh air to keep the heated coil from overheating.

I use this choke assy on the 1405 on my Gladiator. The port is open. Works perfect
Doug

Thanks everyone! I really appreciate the detailed responses. Runs better unplugged, I just wanted to confirm it's purpose.