Fuel Tuning The Electric Choke On Holley 4bl

If I recall correctly, the choke uses an electrically powered heater coil inside the plastic housing. It draws power from the electrical system to heat the coil. When the coil gets hot, it relaxes tension on the choke butterfly and fast idle cam. When It is cold, it causes the choke butterfly to move towards the closed position, and that trips the fast idle cam to increase idle speed.

Check the electrical connections to make sure they are clean and shiny. Check the ground as well. If they check out good, then use a voltmeter to make sure the heater coil is getting the full 12 volts delivered to it.

I do not know what year of car the Holley is on, but I see several possible fixes. First, 15 degrees will bring up problems you may not have seen before. I had to drive a Holley at 9 below this winter. It was just fine at more normal temps, but the choke closed like a clam when that cold. For my car, the low temp uncovered I had the choke a bit too tight.
Now as far as yours closing back up as driving, I wonder if you do not have a full 12v at the positive side or a good ground on the other terminal. If you have a car that had points, do not use the points' wire. Yes, it is switched power, but it could be a resistor wire to prevent the points from arcing and wearing out too quickly. It may not get the choke coil hot enough. On my old car, I ran a separate, fused, new wire from the fuse block.

Make sure the parts are all clean and move freely. There is a high idle adjustment cam with flat steps on it below the choke that can hang up and cause a high idle. I think there is a cork circle on the back of the choke to the body of the carb that if it does not seal will not pull the right temp air over the heated coil. That is less likely than the high idle cam or its adjustment screw.

Now if everything is clean and moves freely (including the high idle cam!) and the power circuit is OK, it could be just on the edge of too tight (closed) and the fresh air across it could be closing it. That is an easy, little three screw adjustment. Small adjustments are the key here and the high idle screw.

Referring to the discussion of modifications to not make, it is a good thing some of us are old enough to have used a carb in a daily driver. My first car had a factory manual choke and no factory seat belts.

Now THAT will help your mileage and power. Good luck finding a full 12v switched wire and happy driving.