Sisson Choke

[meadowbrook]

I wonder what the correct way to start a cold and a hot 1950 dodge with the 230 and a carte bb.

The manual says to pump the gas once to set the choke, the sisson choke literature says not to pump.

Also, what is the purpose of the electromagnetic device in the sisson? It supposedly is to close the choke plate, but wouldn't it be already closed by the thermal spring ?

[Joe Flanagan]

As I recall, as soon as you turn the key, power is relayed to the electromagnet in the sisson choke, which causes it to activate. The small rod on the side of the carb is thrust upward by the action of the electromagnet and engages a cam. The choke plate is then closed. When you release the key, the electromagnet retracts (taking the rod with it) and the thermal spring takes over from there. Others probably are more familiar with its workings but that's how I understand it. 

Edited June 20, 2014 by Joe Flanagan

[DonaldSmith]

The Sisson choke is half-and-half.  The electronic closing is during cranking only.  Once the engine starts, it shouldn't need so much choking.  The bimetallic closing is related to the temperature of the manifold, and eases off as the engine warms up. 

 

Before starting, the accelerator pedal should be pushed enough to set the fast idle.  Pumping the pedal squirts extra gas, which may or not be needed, depending somewhat on the vagaries of the engine.  Trial and error.   

[Don Coatney]

The Sisson choke is half-and-half.  The electronic closing is during cranking only.  Once the engine starts, it shouldn't need so much choking.  The bimetallic closing is related to the temperature of the manifold, and eases off as the engine warms up. 

 

Before starting, the accelerator pedal should be pushed enough to set the fast idle.  Pumping the pedal squirts extra gas, which may or not be needed, depending somewhat on the vagaries of the engine.  Trial and error.   

There is the answer to the question "why push the pedal once"?

[desoto1939]

Sisson Choke: Yes the bimetal plate is heat sensitive. So first of all DO NOT and I say DO NOT ever bend this metal plate.

The starter send an electric charge to the choke and then sets the choke buttlerfly inthe carb. This willhappen when the engine is cold and or hot.

The bimetal spring or metal plate then will hold then choke plate closed and then will slowly allow the plate to retract as the manifold warms up.

If the engine is hot from running then the choke butterfly should retract and take off the choking of the carb.

Very basic in nature. I do have the sisson choke manual saved in a PDF format and saved to CD if anyone needs a copy. I also have the factory testing stand that was used by the dealers to test that the choke was working properly.

As all of you currently know the prices for these old chokes has gone through the roof and the 49-55 sison choke for the Plymouths have gotten out of control and are going in the range of close to 175-200 dollars.

You also need to have the gasket underneath the body of the choke when mounted on the manifold.

I have literature on these chokes and also the adjusting tools. If you want pictures of the tools send me an email

two years ago I did a lecture on the sisson chokes at the AACA annual meeting here in Philadelphia. I am not an expert but have some knowledge on these chokes.

Rich HArtung

Desoto1939@aol.com

[Darbone85737]

I'm curious as to the purpose of the gasket under the choke. Is it merely an insulator from the heat of the manifold?  If so will not using the gasket cause the bi-metallic strip to warm faster and open the butterfly sooner ?