Sisson automatic chokes

[Lou Earle]

I have one of these and was wondering how well they work? anyone have any experience with them? Also what is the wiring on them - to solenoid?

Lou

[Plymouthy Adams]

Lou..once set up right they work well...the engagement of the solenoid is activated with the starter motor that allows full engagement of the choke...once started the tension to the choke is lessened with the dropping of the voltage to the solenoid..this is your basic primary choke divorce...this now reverts to the air gap need in the throat of the carb to ensure running when cold without over enrichment...full divore is the result of the choke bi-metal spring as it loses its tension when heated...at full temp the metal should be fully expanded and the choke valve a perfect vertical position.

[Guest Nile Limbaugh]

Mine works as it's supposed to with the exception of closing too tightly initially, at least for this climate (N. Georgia). But by adjusting the unit slightly that problem is easily overcome.

[bob westphal]

The one that is on the '47 DeSoto works very well now that I figured out how it works and how to hook up the electrical wiring.

[De Soto Frank]

A few thoughts on the topic:

The Sisson choke is a "hybrid": part thermostatic spring/part electro-magnet.

When the engine is cold, a properly set Sisson will close the choke about halfway when the accelerator is depressed to the floor. This initially "sets" the fast-idle cam.

When the starter is engaged, the electromagnet in the choke unit is energized, and closes the choke the rest of the way. When the engine fires and the starter is released, the choke butterfly drops back against the bi-metal thermostat spring, and then gradually opens as the engine warms-up.

Unlike the Carter Climatic Control ( Black bakelite cap on the side of the carb air-horn) and later auto-chokes, there is no vacuum choke pull-off: the Sisson choke set-up is designed to open-up due to gravity acting on the weight of the choke linkage and incoming air rushing past the choke plate tending to force it open.

Most issues with the Sisson choke fall into one of the following catergories:

1) Electromagnet disconnected or failed. The wire should run from the choke unit to the Starter terminal ( the big motor terminal that is energized ONLY when the starter is operating).

2) Incorrect adjustment: any factory shop manual or MoToR's manual of the 1935-1950 period should have proceedure for adjusting the choke...

Most folks that are un-acquainted with the Sisson choke make the mistake of adjusting them so that they fully close on the bi-metal thermostatic spring alone: this results in an incredibly over-rich mixture during warm-up - the car will usually start once, then loads-up and dies and usually gets flooded during attempts to re-start.

3) Binding linkage: if the rods and such are bent or extremely rusty, the choke may not close or open properly. A correctly functioning linkage will fall back to completely open on an engine at operating termperature if the throttle is held open and the choke closed with a free hand. The only lubrication (if any) should be powered graphite.

I'm not aware of "left-hand" or "right-hand" variations on the six cylinder MoPars (but I will believe that they exist); the eight-cylinder choke unit was definitely different in apearance, but functioned the same way.

They must've worked reasonably well, as Chryco used them from about 1934 trough 1952 or so...

I never had any trouble from the ones on my '41 De Soto or '48 NYer...

Drove the De Soto last night, after a week's hibernation... started-up as soon as gas pumped up to the carb... about 10-15 seconds...

So far my $25 "blemished" Group 2 battery from August is holding up...

Frank McMullen

[Ed Griffin]

I've seen the chokes on both sides as well. The same carb. only with a differant linkage. Linkage is differant all the way back to the center linkage bolt that goes in the head. I think the reason for this is the changes through the year blocks but either side will do the job.

Frank, thank you for the great information you took the time to post. I learned something from it already. That will go in the file for sure. Eventualy I'll have a complete "how to" to go back to and make use of when needed. Thanks!

[De Soto Frank]

Shel,

Thanks for the pics...

Does your D-24 have a Stromberg carb ?

The Chrysler & De Soto six always(?) had the choke mounted to the rear of the carb...

I didn't have my D-24 long enough to pay much attention to the carb and choke...

Frank McMullen