Choke plate not functioning

JJHstang · Dec 16, 2020

On my 71 Mach 1 with 351 W It seems my choke plate is not functioning correctly. I have a summit racing 4 bbl carb not quite 3 yrs old. Also my idle speed when warm will not reduce. In drive with no gas applied the car will get up to 12 mph.
I do not have a tach or vacuum gauge so I and just going by sound.
I have attached some pics of the choke plate at various stages.
Suggestions?

7991LXnSHO · Dec 16, 2020

Can you post a pic of the carb without the air cleaner on it? I would like to see what model it is and look for oddities.
If it is an electric choke, check the power and ground wires. Also check the terminals with an ohm meter to make sure the choke coil still conducts electricity.
With the car off and cold, hold the throttle open a ways and see if you can move the flap open easily, and if it springs back.
There is likely a high idle stepped cam and screw to keep the idle up while the choke is not fully open. On a Holley style carb, it’s under the choke housing and hard to see. It should move easily with the throttle held open when the choke flap is open.
Then I’d try adjusting the choke coil (choke pull off) so it just barely is closed coil, and see if it opens when warmed up.

JJHstang · Dec 16, 2020

7991LXnSHO said:
Can you post a pic of the carb without the air cleaner on it? I would like to see what model it is and look for oddities.
If it is an electric choke, check the power and ground wires. Also check the terminals with an ohm meter to make sure the choke coil still conducts electricity.
With the car off and cold, hold the throttle open a ways and see if you can move the flap open easily, and if it springs back.
There is likely a high idle stepped cam and screw to keep the idle up while the choke is not fully open. On a Holley style carb, it’s under the choke housing and hard to see. It should move easily with the throttle held open when the choke flap is open.
Then I’d try adjusting the choke coil (choke pull off) so it just barely is closed coil, and see if it opens when warmed up.

JJHstang · Dec 16, 2020

I went out and moved the throttle, the plate which was open as in the pic. The plate suddenly flipped completely shut and moves freely open and shut by hand.

7991LXnSHO · Dec 16, 2020

Thanks for the pics of the carb. It looks like a Holley with a top plate rather than detachable bowls, so my suggestions fit. You can see the high idle cam behind the choke in the third pic. It’s red.
The electric choke looks like it’s mark is near the middle? Unless it is warm outside, I’d expect the flap to be closed tighter at that adjustment. Besides the questions above, does it have a full 12 v switched power wire to it? I have seen one tapped into the ignition wire on a points car. It was a resistor line, and that did not get hot as fast as it should have.

7991LXnSHO · Dec 16, 2020

JJHstang said:
I went out and moved the throttle, the plate which was open as in the pic. The plate suddenly flipped completely shut and moves freely open and shut by hand.

I was typing as you were. That’s good so far. Now to make sure the electric choke coil is powered and good, then adjustment time.

JJHstang · Dec 16, 2020

Thank you, It is not warm, 50 degrees or colder in my garage. It never opens up when warm either as shown in the first pics. Maybe opens 1/2 to 3/4 inch and never closes tight.
When I bought the car it had a Ford 2 bbl carb with an adapter. There was a small metal tube that brought warm air to the choke (not electric). It broke off not to long ago. A mechanic I know told me it is not needed with the electric choke. I wonder, when it broke off it was in the 90 to 100 degree temp here in Texas. When the new carb was installed on 12/04/17 it was cold and had the small heat tube. I didn’t start to notice the high idle and the choke plate not opening or closing until after it cooled off this late fall. I will borrow an ohm meter and read up on adjusting the choke and idle.
The high idle cam you mentioned is to the right of the choke just below it?

7991LXnSHO · Dec 16, 2020

Yes to the high idle cam. After you have the choke plate functioning right, there is a screw on the throttle shaft passenger side linkage you can adjust if it needs more or less throttle with the choke. It takes a screwdriver from the back side and contortionist unless you hold the throttle so the screw is at a better angle.

With the electric choke there is no need for the hot air tube, at least there in usually no place to hook it up to on the new carb. Hopefully, after you confirm power and continuity, you just need to turn the choke coil back a mark at a time until it opens when warm and still closes when cold.

Choke plate not functioning

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