73 H code idle solenoid

[73pony]

On my 73 H code there is a small solenoid/actuator deal by the carb linkage. My idle is around 625 - 675 rpm and smooth normally. Once in a while the idle kicks up to close to 1,150 rpm. I noticed that this actuator is actually pushing the throttle ahead when activated. If I pull the plug on it the idle goes right back. I believe this had something to do with emissions maybe? Any harm if I disconnect? It is rather annoying.

 

[rocket366]

Is for A/C when activated IMO. But I need BU on this from other forum members.

Paul

 

[73pony]

It comes on when my AC is off. Which is all of the time right now as it doesn't cool at all. And should it almost double my idle speed?

 

[jbojo]

Not sure if I am 100% correct here but this is what I found while researching the subject in the past. For the 70's emission cars with fuel octane ratings going down and higher timing cars tended to diesel when the ignition was turned off and keep running. To compensate for this was to use the idle solenoid. When the ignition was turned on the solenoid would energize and push the carbs butterfly open to a preset point that was usually the idle preset rpm point and when your car was on and foot off the pedal the car would idle normally. When you turned the car off the solenoid would de-energize so the carbs butterfly valves would close fully and essentially choke off the motor by restricting the airflow/fuel though the carb.

Without these solenoids the butterflies would remain at the position required for idle and when you shut off the motor air/fuel would still enter the combustion chambers and the dieseling would just continue.

I experienced this problem when I tried putting on a Holley carb without this solenoid shortly after buying my car and it diesel'd alot. After I put the 4300D back on with the solenoid it worked just fine. I did this before I knew any better.

Hope this makes sense.

 

[73pony]

It only comes on once the engine is warmed up. When you first start and the motor is cold it does not energize and idles fine.

 

[jbojo]

It only comes on once the engine is warmed up. When you first start and the motor is cold it does not energize and idles fine.

I looked at the electrical schematic and the Idle Position Solenoid appears to be activated when the ignition switch is in the run position only. Maybe Midlife can add more here.

 

[midlife]

No I can't offer more than what was stated here. It was used for emissions/anti-dieseling starting circa 1970 on Fords.

 

[rocket366]

I remember some of those solenoids were adjustable by the hex on the end of

the actuator shaft?

Paul

 

[Stocktrader]

jbojo is right. Set the idle with the solenoid. Make sure it is energized when doing so. Once the ignition is shut off the solenoid dis-engages and fully closes the carb to keep the engine from dieseling.

I've added the feature to any carb I use. Just works well.

 

[will e]

right. It has nothing to do with the AC. It is an anti-dieseling device.