1972 fast idle solenoid on carb

[Cleg]

The solenoid valve on the top rear of my carburetor was wired into the ignition system so it is always on when the truck is running. This can't be right but I cant find a good wiring diagram. Can anyone tell me what is supposed to control the solenoid? Thanks.

Cleg

 

[RicardoJM]

If your carb is the original Aisan that came in a 1972 FJ40, that is your Idle Cutoff Solenoid. The Idle Cutoff Solenoid should have power while the ignition is in the run position. When power is provided to the solenoid, it retracts a needle that opens the idle circuit of the carb. When power is removed from the solenoid, the needle pops out and closes the idle circuit. The ignition switch is what controls the solenoid; ignition off should be no power to solenoid, ignition in run position should have power to solenoid.

 

[Cleg]

They must have been smoking something funny at Aisan

Thank you. That is how it is wired but it still makes no sense to me.
That means the solenoid is always energized as long as the ignition is on and only off when the engine is not running.

Why should it need a solenoid at all ? When the engine is not running it shouldn't be sucking any fuel through the idle jet.

Curious.

 

[ColonelMustardFJ40]

The purpose of the idle solenoid it to prevent run-on. When you shut the engine off and it is hot, the solenoid stops all fuel from getting into the idle circuit and therefore prevents dieseling.

 

[Cleg]

Re: Idle solenoid

Thank you. I rebuilt the carb with great care to get every setting precisely per the book but it only ran well with the solenoid energized. I was sure that could not be right and was afraid the solenoid would burn out being on all the time. As is probably the case with most 40 year old vehicles, anything on it could have been messed with or jerry rigged at some point so I had no way of knowing for sure how it was supposed to be wired.

Last year I rebuilt the entire drive train and did a 4 speed conversion with a lot of head scratching along the way. I could have saved myself a lot of trouble by asking a few questions on this forum.

Thanks again.

 

[RicardoJM]

...Why should it need a solenoid at all ? ...

Fair enough question, unfortunately I'm no help with the answer.

I rebuilt the carb with great care to get every setting precisely per the book but it only ran well with the solenoid energized. I was sure that could not be right and was afraid the solenoid would burn out being on all the time. As is probably the case with most 40 year old vehicles, anything on it could have been messed with or jerry rigged at some point so I had no way of knowing for sure how it was supposed to be wired.

Last year I rebuilt the entire drive train and did a 4 speed conversion with a lot of head scratching along the way. I could have saved myself a lot of trouble by asking a few questions on this forum.

Thanks again.

Nice work on rebuilding the carb and kudos for following the specifications. Yeah, with vehicles this old, you really don't know for sure what has been changed on them. This forum is a great resource and I've learned much from it.