how does automatic choke work??

[Alexander]

Hello guys

quick question: how does the automatic choke on a 51 dodge work? I cant seem to figure it out. When the ignition is on and the engine is hot, should there be power at the choke? Does the power at choke stop when the engine gets hot? or is the choke mechanical with a bi-metal mechanism. what will cause the choke to open when the engine gets hot. I take it there is an electro magnate inside?

If any one has a quick moment to explain from the point the car is cold to the point when the engine get hot (eclectically and mechanically).

Thank you.

Alex

[55 Fargo]

According to my Chrysler shop manual, it is a hair pin shaped thermostat in the housing of the auto-choke, the electrical function closes the choke when the engine is cranking, when the engine is cold. The thermostat gets heat from the manifold, whcih heats it up and keeps the choke open when the engine is at operating temp. Hope this helps.........Fred ps, if you need to know how to adjust your choke,I can post that also

[TodFitch]

Hello guys

quick question: how does the automatic choke on a 51 dodge work? I cant seem to figure it out. When the ignition is on and the engine is hot, should there be power at the choke? Does the power at choke stop when the engine gets hot? or is the choke mechanical with a bi-metal mechanism. what will cause the choke to open when the engine gets hot. I take it there is an electro magnate inside?

If any one has a quick moment to explain from the point the car is cold to the point when the engine get hot (eclectically and mechanically).

Thank you.

Alex

Caveat: I don't own one of these nor have I ever. So I don't really know what I am writing about. That said. . .

The 1946-54 Plymouth factory service manual has a test and adjustment section on the choke. Unfortunately they don't have a "theory of operation" in there. However there is an illustration with two key pieces of text.

There is an arrow to an electrical coil with text that says "electromagnet energizes when starter is on".

There is another arrow to a bi-metalic strip that says "bi-metal thermostat contracts as it is warmed".

Given this I think the unit sets itself when you start the engine then uses heat to release the choke.

[Alexander]

Thank you Fred & Tod. between your 2 explanations I think I now understand

Cheers

Alex

[DonaldSmith]

From 2004, 06/14, by Frank McMullen

"How to adjust the Sisson electric choke, Chrysler products 1935 -mid-'50s...

Modern auto choke, thermostatic spring, closes FULLY when engine is cold (depress the accelerator fully to floor once, then release - allows choke and fast-idle cam to "set"); then when the engine starts, a vacuum piston or pull-off diaphragm opens choke part-way to pre-determined setting, providing a suitable mixture for the engine to run on as it's warming-up. As engine & manifold heat-up, choke thermostat spring relaxes, until choke is wide open.

"Now, here's where the flat-head MoPar system is different: when correctly adjusted, the thermostat spring in the choke housing down on the manifold closes the choke valve just PART-WAY with a cold engine. There is a wire running from the choke housing over to the starter relay: this wire energizes the choke electromagnet when the starter is operated...this FULLY closes the choke when starting the cold engine.

"When the engine fires, and you release the starter button, the electromagnet is de-energized ,and releases the choke back to that part-way warm-up position. From then on, the operation is just like the "modern" auto-choke: as the engine warms-up, that thermostat spring relaxes, and the choke opens.

"Most folks misunderstand how the Chrysler choke operates, and they adjust the arm on the choke unit so that the t-stat spring closes the choke fully...then the car is way over-choked, runs awful and belches black smoke until it warms-up.

"(Aw heck...I'm this far along...)

"Correct adjustment is obtained thus:

"Remove the air cleaner from the carb.

"On the choke unit mounted on the manifold - on the side opposite the operating lever, the choke shaft sticks-out of the housing a bit...you will notice a hole drilled through the choke shaft...find a drill bit that just fits through that hole (shank-end first) - this will probably be a 3/32" or 1/8" drill...you will also notice a notch in the choke stat case which the hole in the shaft will line-up with. Disconnect the choke link rod from the operating arm of the choke unit...move the arm as required until you can insert the drill through the choke shaft until it engages a notch in the bottom of the choke unit housing.

"Next, close the choke butterfly via the rod which you disconnected from the choke stat arm...(you may have to open the throttle slightly to allow the fast-idle cam to move and the choke to fully close)."

(I hope this helps.)