choke does not close!

Back again. The butterfly choke NEVER closes on my 49 DeSoto. It is automatic - controlled by a device (thermostat?) attached to the exhaust manifold. I've had to use starter fluid on some of these (now colder New Hampshire) mornings - then it fires right up- AND it starts nicely (without starter fluid) at the end of the workday for the drive home. It seems to stay at an approx. 35 degree angle from the horizontal.

All the rods, etc attached to the carb seem to move freely, & are clean & dry.

I've heard these early automatic chokes tend to malfunction.

Is this the problem? Should I get the thermostat replaced/repaired? I've also heard that some people go back to retrofitting a manual choke. Any advice would be most appreciated.

I removed the air filter tonight, & placed a block of wood over the carb. Tomorrow morning, I'll try to start it for the commute, hoping my makeshift closure will preclude the need for starting fluid.

Stan

Your automatic choke is a "Sisson" thermostatic/electric choke, and they are extremely reliable. Proper adjustment procedure is given in Motors Manuals of the era and many other places and I suggest you try the adjustment if you haven't done so already. It's been about 40 years since I did one, but as I remember there is a small hole in the protruding end of the shaft, and a notch in the base below it. Using a steel pin or drill of proper diameter you insert it through the shaft hole into the notch in the base and with the mechanism fixed in that position, adjust the linkage to give either full closed or full open (not sure which, but it should be obvious when you look at it) position.

PS - just checked Motors Manual; with the shaft pinned in the adjustment position, adjust the linkage to give a fully closed choke valve.

There is/should be a wire from the starter to the choke that actuates a solenoid inside the choke body to close it when you are starting. You might also want to check that it is properly wired, etc. Check you factory service manual of the after market manuals of the era for how it should be wired.

As the other guys have mentioned, there's an electromagnet that fully closes the butterfly when the starter is engaged.

When properly adjusted, the thermostatic spring NEVER closes that choke butterfly more than half-way.

When starting the cold engine, depress the accelerator to the floor fully and release: this allows the thermostatic spring to set the choke and fast-idle cam, then when the starter is engaged, the electromagnet closes the butterfly fully. When the engine fires and the key is released, the choke falls back against the thermostatic spring, via gravity.

As the engine warms-up, the thermostatic spring relaxes, allowing the choke to open fully.

When all the components are working and properly adjusted, it is indeed a very reliable system.

Not trying to be harsh, but many aspects of these pre-1955 MoPars are NOT like their counterparts found in later Ford / GM / MoPar vehicles... but they ARE common across MoPar-dom from about 1935-1954... The Sisson electric choke and Fluid Drive/ Tip-Toe shift transmissions are two examples.

Suggest you obtain a factory shop manual ( original or re-print) or at least a MoToR's or Chilton's shop manual that covers your era, and read-up on the various operating systems and develop an understanding of how they work...

Another issue that contributes to "hard-starting", particularly if the vehicle has sat for a couple of days is the carb going dry ( thank you modern fuels !)... it takes some extra cranking or starting fluid to fill the carb back up.

But check the choke adjustment first and that the electromagnet is working.

Try adjusting the choke, do a search in the Chrysler section or maybe DeSoto, I know I covered this before.

If the Sisson choke is worn out NOS ones come up on Ebay once in a while. Or you could change to a hand choke. I recommend keeping the original system. It is very simple and trouble free and works well. Of course anything can wear out after 60 years.

Thank you Owen Dyneto, ply33, and De Soto Frank,

I have a reprint of the shop manual, I read the carberator section, but now that I know what I'm looking for, I'll reread it.

I'll also check for the wire from the starter to the choke.

If I'm reading what Frank wrote correctly, am I correct in assuming that I'd never be able to SEE the choke closed? (Unless another person were to start the car while I looked at the choke).?

Nice to know these were reliable - sounds like an ingenious mechanism.

I never IMAGINED that the choke was electric withan electro magnet

OwenDyneto referred to a "Motors Manual" - can I look this up online? Is it different from the "shop manual"?

BY THE WAY, if this IS electromagnetically controlled, it won't be the only thing on the car that is - HAS ANYONE EVER HEARD OF AN ELECTROMAGNETICALLY - RELEASED GAS CAP? With the power on, I press a small button under the dashboard to release the gas cap. (It may or may not be magnetic, but it is electrically controlled.)

ss

Stan,

Yes, there was an aftermarket (?) electrically-released locking gas-cap for MoPars.

MoToR's was a publisher of automotive repair manuals from the late 1930's thru the 1970's... they are big hardbound volumes, usually with green (through 1943 at least) or blue (1940's- on) cloth bindings with gold stripes across the spine. They cover all American makes common in whatever range of years is encompassed by a given edition.

They are quite common at swap meets, usually going for anywhere between $2 and $25 a copy. Suggest looking for one that covers 1940 - 1955 or there abouts, but that at least includes 1949.

You are correct that it is usually a two-man job to witness the choke actually being fully closed, although if you remove the air-cleaner and look carefully between the cowl the the edge the open hood as you hit the starter, you might see the linkage moving ot close the choke. You could also test the electromagnet itself by running a jumper wire from the "hot" terminal of the battery (negative in this case) to the terminal on the choke solenoid: the arm should move upwards. Note - the solenoid does not have enough ooomph to close the choke AND raise the fast-idle cam against the pressure of the idle-stop screw, so you will probably have to open the throttle a bit while checking the choke solenoid.

I drove a '48 New Yorker some 40,000 miles while in College and have put nearly 30,000 on my '41 De Soto, and never had issues with the chokes... with this exception: since the choke closes with activation of the starter, it is possible to flood the engine if you pump the accelerator too much... if this happens, you have to pull the air-cleaner and block the choke open and crank with the throttle open until the flooding clears. Once you've determined your De Soto's favorite starting proceedure, this probably won't happen.

As the other guys have mentioned, there's an electromagnet that fully closes the butterfly when the starter is engaged.

When properly adjusted, the thermostatic spring NEVER closes that choke butterfly more than half-way.:confused:

When starting the cold engine, depress the accelerator to the floor fully and release: this allows the thermostatic spring to set the choke and fast-idle cam, then when the starter is engaged, the electromagnet closes the butterfly fully. When the engine fires and the key is released, the choke falls back against the thermostatic spring, via gravity.

As the engine warms-up, the thermostatic spring relaxes, allowing the choke to open fully.

When all the components are working and properly adjusted, it is indeed a very reliable system.

Not trying to be harsh, but many aspects of these pre-1955 MoPars are NOT like their counterparts found in later Ford / GM / MoPar vehicles... but they ARE common across MoPar-dom from about 1935-1954... The Sisson electric choke and Fluid Drive/ Tip-Toe shift transmissions are two examples.

Suggest you obtain a factory shop manual ( original or re-print) or at least a MoToR's or Chilton's shop manual that covers your era, and read-up on the various operating systems and develop an understanding of how they work...

Another issue that contributes to "hard-starting", particularly if the vehicle has sat for a couple of days is the carb going dry ( thank you modern fuels !)... it takes some extra cranking or starting fluid to fill the carb back up.

But check the choke adjustment first and that the electromagnet is working.

The instruction to adjust the choke say to make the choke "closed tight" and then tighten the adjustemt to the arm.

INSTRUCTIONS

FOR ADruSTME}IT

AC-758 AND AC-7588

1. Open hand throttle approximarely onefourth

way.

2. Remove air cleaner from carburetor so

you can observe position of choke valve in

carburetor.

3. Move Automatic Choke lever unril hole

in brass shaft lines up with slor in bearings

and insert adjusting tool C-723 through hole

in shaft (as illustrated). Push adjusting tool

all the way down to engine manifold so rhat

it engages in notch in base of Automaric

Choke.

4. Loosen clamp screw on Automatic

Choke Lever, using wrench C-777, and push

the lever upward unril carburetor choke

valve is closed tight. Hold

the lever in this position and

tighten clamp screw in lever,

then relnove adjusting roo[.

5. R"place air cleaner,

checking to be sure that

tightening of air cleaner

clamp did nor bind choke

valve or shaft.

6. See that there is no binding in the fasr

idle or choke mechanism rhar *o.tld interfere

with free operation of carburetor choke

valve. Always check this with carburetor

throttle partly open.

There was a Mopar branded electrically released gas cap in that era. Not sure if it came from the factory or was a dealer install option though. $0.25/gallon gas might sound cheap to us to day but adjusted for inflation that is not much different that what gas costs nowadays.

You can buy a NOS MoPar electric gas cap on ebay for around $140.00. I have a couple cars that have an elecric gas cap.

I worry that they will blow up the car some day.