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The wire from the choke pull-off runs directly to the starter on my '51 Wayfarer which the wiring diagram shows is correct. Does this energize only while the starter is operating and, if so, how does it open the choke? Or does it rely more on manifold heat?



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According to Donald Smith at the P15-D24 forum:


"How to adjust the Sisson electric choke, Chrysler products 1935 -mid-'50s... 
Modern auto choke, thermostatic spring, closes FULLY when engine is cold (depress the accelerator fully to floor once, then release - allows choke and fast-idle cam to "set"); then when the engine starts, a vacuum piston or pull-off diaphragm opens choke part-way to pre-determined setting, providing a suitable mixture for the engine to run on as it's warming-up. As engine & manifold heat-up, choke thermostat spring relaxes, until choke is wide open. 

"Now, here's where the flat-head MoPar system is different: when correctly adjusted, the thermostat spring in the choke housing down on the manifold closes the choke valve just PART-WAY with a cold engine. There is a wire running from the choke housing over to the starter relay: this wire energizes the choke electromagnet when the starter is operated...this FULLY closes the choke when starting the cold engine. 

"When the engine fires, and you release the starter button, the electromagnet is de-energized ,and releases the choke back to that part-way warm-up position. From then on, the operation is just like the "modern" auto-choke: as the engine warms-up, that thermostat spring relaxes, and the choke opens. 

"Most folks misunderstand how the Chrysler choke operates, and they adjust the arm on the choke unit so that the t-stat spring closes the choke fully...then the car is way over-choked, runs awful and belches black smoke until it warms-up. 

"(Aw heck...I'm this far along...) 

"Correct adjustment is obtained thus: 

"Remove the air cleaner from the carb. 

"On the choke unit mounted on the manifold - on the side opposite the operating lever, the choke shaft sticks-out of the housing a will notice a hole drilled through the choke shaft...find a drill bit that just fits through that hole (shank-end first) - this will probably be a 3/32" or 1/8" will also notice a notch in the choke stat case which the hole in the shaft will line-up with. Disconnect the choke link rod from the operating arm of the choke unit...move the arm as required until you can insert the drill through the choke shaft until it engages a notch in the bottom of the choke unit housing. 

"Next, close the choke butterfly via the rod which you disconnected from the choke stat arm...(you may have to open the throttle slightly to allow the fast-idle cam to move and the choke to fully close)."

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Your are most welcome - even if I wasn't the author of the information I sent.  I wish you luck with you choke adjustments.  You wouldn't happen to have a spare Sisson electric choke just hanging around would you?  Mine isn't working.



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