Sisson Chokes - A Technical Study

[keithb7]

I am interested in learning more about how and why the sisson choke functions. I have a pretty good grasp on the choke operation itself, it's the sisson actuator that I am interested in studying. A sisson is utilized in my 1938 Chrysler. I am not sure it's working, so it seems like a good opportunity to dig in.

 

I studied my shop manual. From what I can decipher is:

 

- 6V is at the starter lug, standing by, directly from the battery

- turn the ignition key on. 6V passes thru the ignition switch from the ammeter to the ignition coil. This excites the coil primary windings. 6V also now goes to the fuel gauge. The       ammeter is also hooked up to the same lug on the starter, as the battery cable. It's hot all the time waiting for any opportunity to go to ground.

-Push the starter button on the dash. This switch now passes thru 6V pulled from the now energized fuel gauge, to the starter solenoid

-The starter solenoid is energized and closes a set of contact points (or relay) . These contact points now activate a larger magnet coil, activating the starter to turn, cranking the engine

- 6V for the sisson choke is supplied via the relay contacts in the starter solenoid. When the starter button is activated, closing the starter solenoid contacts,  the starter is now turning,  This is the only time 6v is sent to the sisson choke. 

- Inside the sisson choke is another coil. It is excited by the 6V via the starter solenoid. The sisson choke coil is grounded via the exhaust manifold. The coil when excited, moves the choke linkage. The choke closes to the pre-set point while the engine is cranking over to start.

 

Questions:

 

- When you let go of the starter button, 6V is cut off to the sisson choke. What keeps the choke engaged? Some sort of internal linkage I assume?

 

- The sisson choke is bolted directly to the exhaust manifold. I assume as it heats up, some type of bi-metallic spring inside the choke housing releases tension on the choke linkage, to open the choke valve at the carb intake?

 

I tried applying 6V directly from battery, via an overlander wire, to the sisson choke. Sparks flew. Choke linkage did not move.  Is this a good indicator that there may be an internal ground, allowing high amp draw? Indicating a failed coil inside the sisson choke? I could try it again, leave the wire there and see what melts. Lol.

I've got more troubleshooting to do with my muti-meter.

 

Any help is appreciated. Thanks.

Keith

 

 

 

 

Edited June 15, 2021 by keithb7

[keithb7]

 

 

Edited June 15, 2021 by keithb7

[chrysler1941]

Here is a description from shop manual

 

"An automatic choke controls the mixture of
gasoline and air at the carburetor according to
the temperature of the engine, and operates when
starting and during the time the engine is reaching
operating temperature. After the engine is
warm (due to the heat of the exhaust manifold
affecting the choke) the choke valve opens and
stays in this open, or "off" position until the
manifold cools."

 

There is much more in manual about adjustment etc,

 

Sisson choke is mounted on a asbestos gasket and is important to reflect heat and operation

[Plymouthy Adams]

the term you using 'passing through' on components listed is not correct...these are only common tie points for power distribution...if the voltage and subsequent current associated with the circuit passed through....that load would fry a few of your components immediately.  AS for the sissions....you are transferring voltage from the starter side of the relay to the coil of the choke...where upon you set the high cam with you foot/accelerator and let up the pedal while turning of the started is taking place....this locks the choke closed and high cam for proper idle speed...if you do not allow the high cam to set...the circuit when deenergized will have no continued effect on choking.

[chrysler1941]

[Sniper]

I think that the choke is held open by the unenergized solenoid setup in the choke housing.  Upon starting the solenoid releases it's hold on the choke and the bimetallic spring wants to keep the choke closed, as the spring heats up via manifold heat it wants to open the choke.  Once fully open the unenergized solenoid once again holds the choke open until the next starting cycle. 

[greg g]

The stove, bimetal spring, linkage and housing function as the choke pull off (open) as the Manifold warms. The shot of electric from the starter solenoid is the pull on (butterfly closed) I believe the high idle cam serves as the hold closed till the bimetal begins the opening sequence and becomes the hold open till cooled off.

[desoto1939]

Yes everyone is correct on the sisson choke. It is important to note that you do need the gasket under the choke body.  But do not ever bend the bi-metal spring of the choke. If you do it will then mess up the function of the choke.

 

I do have the sisson choke testing stand and the adjusting tools.  I also have several of the factory pins or rods that are used to set the choke up properly.

 

I will try to upload some printour from a seminar that I did on these chokes at the AACA annual meeting.

 

 

Rich Hartung

desoto1939@aol.com

 

 

[Frank Gooz]

Rich,

I would like to learn from this posting how to adjust the choke properly. I tried to adjust the one on my 1950 Dodge do to such a high idle speed.

Now it seems that there is no fast idle/choke function.

Please keep us up to date.

Thank you

Frank

[Marcel Backs]

What is the correct material for the manifold isolator gasket on the auto choke assembly? Direct contact to the manifold is not an option for proper function. It would be better to have a sheet of the material to make many gaskets rather than order one that was stamped out across the pond for 10 USD. Given the state of the supply chain these days, stocking up leads to more autonomy. To actuate the AC on my D14, I think you have to momentarily put the pedal to the metal with the key on to close the choke. Is a heat riser set up necessary for this assembly to operate in spec  and open the choke at the correct time in the warm up cycle?

[DJ194950]

The choke butterfly cannot be moved by the Sisson unless the throttle is slightly opened. ( the idle linkages keep it from  moving). Therefore  you see no movement of the choke rod from it when motor is cold. if throttle is left closed. When the motor is already hot you will see no movement either due to the bi-metal spring inside of the Sisson is totally relaxed= no more choke -as not needed anymore.

 

DJ

[desoto1939]

3 hours ago, Marcel Backs said:

What is the correct material for the manifold isolator gasket on the auto choke assembly? Direct contact to the manifold is not an option for proper function. It would be better to have a sheet of the material to make many gaskets rather than order one that was stamped out across the pond for 10 USD. Given the state of the supply chain these days, stocking up leads to more autonomy. To actuate the AC on my D14, I think you have to momentarily put the pedal to the metal with the key on to close the choke. Is a heat riser set up necessary for this assembly to operate in spec  and open the choke at the correct time in the warm up cycle?

Marcel the heat riser is not connected to the choke  and does not effect the Sisson choke.  The heat riser was set up so that the base of the carb would not ice over during cold weather cars that have cold winter weather. It directed the heat up to the base of the carb to get it warm and stop the carb from icing over. When this happens the car will stall and idle rough inthe winter. As the fuel is  vaporized it will then ice up the base of the carb. 

[Plymouthy Adams]

look into the Garloc line of thermogasket material.....

[desoto1939]

OK I willbe attaching pages from my power point presentation that i did on the sisson choke there are 27 pages worth of information.

 

I do have the sisson choke testing stand and also a 2nd one but that is just missing the thermometer.

 

Also have all of the adjusting tools and several of the setup rod pins.

 

Since the file are larger than the limit now set up on the forum if you want the information send me an email and I will send the documents to you.

 

Rich Hartung

Desoto1939@aol.com

[Marcel Backs]

THANKS!

[chrysler1941]

https://www.ebay.com/itm/184366207270?hash=item2aed151126:g:cF8AAOSwGL5fdLD6

 

 

[keithb7]

I'd be farther ahead if I cut up 2 or 3 $100 bills and made my own gasket. 

 

 

Edited June 15, 2021 by keithb7

[wagoneer]

29 minutes ago, keithb7 said:

I'd be farther ahead if I cut up 2 or 3 $100 bills and made a gasket. 

 

 

Frankly that must just be a scam. Stick it in an envelope and put an international stamp on it and be done - $2

[Plymouthy Adams]

they hoping you did  not see that part......who are these sick people  (quick sniper, name the movie)

 

 

as if we did not know who....

Edited June 15, 2021 by Plymouthy Adams

[Sniper]

Had to google it.

 

I don't watch movies like Dumb and Dumber, which explains why I didn't know the quote.

[RobertKB]

These chokes are very easy to set up. I just followed the directions in my shop manuals for the chokes on my ‘51 Dodge and ‘53 Plymouth. You do need a thin rod to use as a tool. I just used a small finishing nail. 
 

Not much can go wrong on them but the one on my ‘53 Plymouth did need to be changed out. Fortunately I had a spare one from a parts car. Very important to have the right gasket. I think I bought a few from Neil Riddle at Old Plym Cafe. 

[Plymouthy Adams]

46 minutes ago, Sniper said:

Had to google it.

 

I don't watch movies like Dumb and Dumber, which explains why I didn't know the quote.

I am not a Jim C. by any means....but the movie has to be seen about 3-4 times to catch all the things going on in the background that will flat crack you up....Mike Starr is a true character...and as in FUNNY FARM....popping them anti-acid tablets like tic tacs...it is a signature for him....

[desoto1939]

4 hours ago, keithb7 said:

I'd be farther ahead if I cut up 2 or 3 $100 bills and made my own gasket. 

 

 

 

 

This rate is not what the seller is charging it is what Ebay is charging. When you are from a foreign country and you select the United Kingdom the Ebay system automatically enters the shipping fee or $271 dollars.  

 

Ebay is the issue not the seller. Another person also had the same issue and we figured out the reason why the high shipping costs.

 

Do not blame the seller it is Ebay.

 

Try it  where is states ships worldwide on the ebay listing then go to the next screen and select a foreign country and then see what happens to the shipping costs.

 

Rich Hartung

Desoto1939@aol.com

[Frank Gooz]

Would a sheet of material from exhaust/ headers work? I think we can still get this at auto parts store.

[kencombs]

14 hours ago, desoto1939 said:

 

 

This rate is not what the seller is charging it is what Ebay is charging. When you are from a foreign country and you select the United Kingdom the Ebay system automatically enters the shipping fee or $271 dollars.  

 

Ebay is the issue not the seller. Another person also had the same issue and we figured out the reason why the high shipping costs.

 

Do not blame the seller it is Ebay.

 

Try it  where is states ships worldwide on the ebay listing then go to the next screen and select a foreign country and then see what happens to the shipping costs.

 

Rich Hartung

Desoto1939@aol.com

Yep, he is using eBay's worldwide shipping service, not shipping directly, which he should be doing with type of product, small, light, envelop only.

 

Even at that, I'd bet there is something in his input data for the package the triggers that shipping price.  Weight, dimensions, etc, because I tried several countries and they all showed the same price.   Maybe a typo in handling charge?

 

edit just confirmed that probability:  I found an OD solenoid for sale, selected Australia and the shipping cost was under 75 bucks.  Lots bigger, heavier and a box rather than envelope.  the gasket must have a data error.   I've seen guys with an ebay store do things like that when they are out of stock.  Keeps people from ordering, but doesn't cost the owner a store relisting fee.

 

I've sold a lot of items to Australia, Canada and European customers and never used the eBay service and only had one issue.  Italy post lost it.

Edited June 16, 2021 by kencombs