what kind of carb is that for?
IDK - might be associated with a Rochester Quadrajet.
I think that if you bought a Chevy/GMC back then, you would get a carburetor. It might have been a 2 barrel or a 4 barrel, electric or manual choke, etc. - but one thing was for certain; you were going to get a Rochester.
Some carburetors of that era had an idle control solenoid. Depending on the model year, it was used in two, very different ways:
Long explanation by me. I've never even seen one of these, so consider the source:
Originally, it's purpose was to prevent the engine from dieseling (running on after ignition was shut off). It was energized (and stroked out) whenever the key was in the RUN position. It was adjusted so that, when it was energized and the plunger was extended, it held the throttle linkage open enough to produce a smooth idle. When the key was turned to the OFF position, power to the idle stop solenoid was switched off. The plunger would retract - and the throttle plates (assisted by the external linkage springs) would be allowed to shut completely. This prevented any possibility of a run-on condition. Why this feature was considered necessary, your guess is as good as mine.
Later on it was adapted and used to prevent a drop in engine idle RPM when an external mechanical load was applied (read - the A/C compressor clutch pulled in). This was in the days before ECU's. The only input available to indicate a drop in RPM was the pulsed signal from the distributor C terminal (the same white wire used to drive the tachometer needle). The solenoid would be normally de-energized and the plunger would be clear of the carb's idle linkage.
If the A/C compressor clutch pulled in while the engine was idling (i.e. foot off the gas pedal and throttle plates nearly shut), RPM's would drop significantly. The pulsed signal from the tach would drop accordingly. If the signal dropped low enough, the speed switch would close and send power to the idle solenoid. The plunger would shoot out and contact the carb linkage.
There was a basic problem with this design however. The plunger was not nearly strong enough to overcome the spring tension in the linkage. It could only hold the linkage open - not drive it open. So, if the operator noted a drop in engine speed, he would have to depress the accelerator enough that the plunger could get under the throttle arm and hold it there. But the problem was, if he pushed too hard on the gas pedal RPM's could rise above the speed switch cut-out point and the signal to the solenoid would be lost.
Another guy - named Dave - is more articulate than I. He can say the same thing in 4 short sentences:
It depends on the car. On some cars, the idle stop solenoid is connected to ignition power so that the throttle is held open while the engine is running then closes fully when the key is off to prevent dieseling. If that is how yours is wired, it will work for the electric choke. On other cars the solenoid is normally retracted and is only powered under high load conditions, such as when the A/C compressor is on. In that case, it will not be suitable for use on the choke.
