Sisson Confusion

[Joe Flanagan]

Spent yesterday evening messing around with a Sisson choke that actually works. It needed to be cleaned up in order to operate correctly. My question is this: When the electromagnet activates, it closes the choke valve in the carburetor. As soon as you let go of the key, the arm retracts. My question is, is the choke supposed to stay closed? I know that the automatic choke lever cannot overcome the pressure on the fast idle cam and that you are advised to open the throttle a bit when you start the car. So under this scenario, the automatic choke would close the choke valve in the carburetor, and then you would take your foot off the gas and then the valve would stay closed and you'd be at high idle? Wouldn't you be holding the key in the start position too long and grinding the starter?

Or is the choke supposed to flap closed only for that second while you are starting a cold engine and then immediately drop back to its semi-open position?

Totally confused here. By the way, I have read the adjustment procedure and have the choke properly adjusted. Just seems odd to me that the choke valve would snap shut for the second you start the car and then drop back open. That's the way mine is working now and I suspect there is some interaction with the fast idle cam that I am not understanding.

[woodie49]

Joe,

When I adjusted mine to the manual, it seemed to me that the choke is completely closed when cold, even without engaging the switch. It begins to open fairly quickly as the motor heats up. That caused me to assume that the real function of the electromagnetic switch was to go to full choke while the motor was only moderately heated. I am currently using it without being wired up, and it is working great on both cold and hot starts.

When I changed my carb, the linkage arm was about a quarter inch too short, so I have to make one, which could be causing my choke to operate a bit differently. I note in the choke manual that there are two arms for the sisson, I assume one is a bit longer that the other, but I do not have both to compare.

Once the sisson heats up completely, the spring is sufficiently relaxed that the choke does not close even when the sisson is powered.

[Joe Flanagan]

I just went out to check and it turns out I was wrong. I did not have my choke adjusted correctly. With a cold engine, it was sitting about 2/3 open. I adjusted the choke, then started the car, and gradually, it moves to its full open position, so I know the bimetallic spring inside the Sisson choke is working correctly. Also, when I turn the key, the arm snaps up as it should, so I guess I am officially over this particular hurdle. Even if I don't understand exactly how it all works. The car starts nicely and idles nicely, too. Acceleration is smooth.

[desoto1939]

Joe. Is the choke that I sent you the one that you now have onthe car? If it is I am glad that it is working for you.

Rich Hartung

[48mirage]

To adjust the sisson on my D30. After removing the aircleaner block the throttle open about 1/3 open. Move the choke rod until the hole on the opposite side of the sisson aligns with the hole in the brass bearing. Put a pin in that hole so that it holds the sisson in that position. Loosen the clamp screw connecting the sisson to the choke rod. With your finger close the choke butterfly and tighten the clamp on the choke rod. Make sure there is no slop in the clutch rod and remove the pin that held the sisson in position. You should be ready to go. This can be done engine hot or cold.

[Joe Flanagan]

Yep, that's what I did.

Yes, Rich. It's the choke I got from you. I took the linkage apart and cleaned everything up. Works very well.

[Tom Skinner]

Gents,

A little trick I learned when adjusting the Sisson Choke. Instead of blocking the throttle open 1/3 the way - simply unhook the accelerator spring and it will just lay in the 1/3 open position. Now pin up your Choke and adjust.

It certainly leaves you an extra free hand this way and no acrobatics are necessary:)

Tom