Re: [FWDLK] Auto Choke

In a message dated 9/6/2004 8:59:14 PM Eastern Standard Time, Woomerj writes:

Thanks very much for the help. You have me going in the right direction. I have two more questions.

1. Is there a vacum port inside the carb that helps to suck the hot air thru the tube that loops down thru the manifold, or does the hot air come up thru the tube naturally because hot air rises?

Jim,

The path of the heated air from the exhaust manifold is into the choke housing where it warms the bi-metallic choke coil, then to the "Choke-pull-off piston", then down through the main body and the throttle body to a port BELOW the throttle plate. Therefore, it sees manifold vacuum at all times.

During the periods of time when the throttle is open (Road load and Wide Open Throttle (WOT)), airflow through the carburetor throttle body tends to "Blow" the choke blade open against the force of the bi-metallic choke coil and the engine receives a richer-than normal mixture to keep running when the engine is cold.

When the engine is idling, there is not enough airflow around the throttle plate to keep the choke plate open. That is when the manifold vacuum is highest, and it is applied against the choke pull-off piston, which prevents the choke plate from closing completely and flooding the engine, which would cause it to stall.

There is one more choke control mechanism. That is the "Choke Unloader". If an engine floods when cold, there must be a way to open or "Unload" the choke so as to clear the engine while cranking. This is accomplished by a portion of the leverage that pushes the choke plate partly open when you open the throttle all the way. Thus the instructions when you flood the engine to "Hold the throttle wide open without pumping and crank the engine over".

In the wide open throttle position at cranking speeds there is not enough airflow to make the main system flow fuel, and the throttle plate is too far away from the idle ports to make them flow fuel. With the choke held open you will soon clear the engine of unburnt fuel.

Question # 2.

I rotated the bakelite housing until the choke just closed. The indicator on the movable bakelite housing was at about 2:00 o'clock and would only go slightly more. It was way past, to the right,of the indicating lines on the stationery bakelite housing. Does that indicate the coil was put into the housing incorrectly?

These cabs were just rebuilt and they may have made a mistake when they put them together.

Jim, if you remove the black choke coil housings you will note that the coils are simply slipped into the end of a slotted shaft. They frequently fall out after they have seen some service. If you think about it, you could install them in four different ways, depending upon whether you either rotate the housing 180 degrees you could put them in two ways, and/or "Flop" the coils over, two choices, again.

What to do? Look at the end of the coil. It has a 90 degree hook on the end. The coil must be put in so that the hook will PULL the actuating lever on the choke lever arm to close the choke.

Next decision: Put the coil into the housing so it will PULL the choke closed. (It is not necessary to put the three screws in just yet.) With the throttle held PARTLY open so that the fast-idle cam is not in the way, and the choke plate is free, put the housing in place and slowly turn it so as to close the choke. (Sometimes it might make things easier to slightly file the O.D. of the bakelite to make it easier to turn.) Rap the carburetor so as to overcome friction. When the choke is closed, you SHOULD be about in the middle of the adjustment. If you are not, remove the choke coil housing and remove the coil, replacing it 180 degrees from where it was. The scale should be OK, then.

Something else to remember: These things have been out in the field for over 40 years. It is very possible that the bimetallic coils have been replaced by other than standard parts. (They came in different strengths.) The primary thing to remember is that the basic setting is usually "One notch richer than it takes to close the choke plate completely at room temperature." All else is mostly cosmetic.

Good Luck! These are simple mechanisms once you understand them. Let us know how you do, and don't be afraid to ask more questions.

Anddddddddd, the Mighty Chrysler lives again. I transplanted the wedge engine into the '57 with a rebuild, and the transmission acts just like a new one.

Thanks again,

Joe