I have never used a Carb with an Electric Choke. Now I have one and am wondering the best way to energize it. If it is hooked up with a constant 12 volts from an ignition-on point, does this mean that the choke is to stay energized the whole time you are driving the car. And does this mean that it needs the 12volts not only to actuate its use but also to keep it in the wide open position after the thing has warmed up.
Conversely, I have contemplated energizing the electric choke mechanism by having the 12 volt source on an on/off switch inside the car and only turning it on when I need it. And if used this way, i intended to turn it off after the engine is warmed up. But if it needs the 12volts on to hold it in the open position then this won't work.
Can anyone tell me just what the feature is of how the electric choke works. Thanks, Dave.

 

The electric choke is a bimetallic element that is heated by having electricity run through it.

I'm sure having the engine on will keep it somewhat warm, but probably not enough to completely close the choke. That element gets pretty hot, hotter than I suspect the surface of the carb to be.

My favorite way of doing this that I've seen is to set up an always hot 12V source and run it through an oil pressure switch - then the choke will only start opening when the engine detects oil pressure.

 

The choke will need 12 volts all the time the engine is running or it will cool off and close again.

 

There is a spring coil inside the electric choke that when you apply 12V to it, it will cause the spring to expand. This will force the choke to slowly turn off. This is usually around a minute or less. If the engine is running on the fast idle cam it will continue to run at a fast idle until you tap the excel pedal which causes it to come off of the fast idle cam. After the engine warms, heat from the small riser tube from the intake will heat the choke coil to keep it warm to keep the choke off while the engine is warm. You wouldn't want it to choke the engine again the next time you start it after getting ice cream and the engine is still warm.

I have the very same issue as you. I looked and scoured the wiring diagrams to find a good source of ignition to wire the electric choke to and could only come up with a few things and neither is what I really wanted. One is the hot side of the coil before the ballast. If you are running OEM, the wire itself is the ballast resistor and you cannot connect anywhere because you will not have 12V and you will load down the ballast wire. Other than that, there is NO 12V ignition under the hood that I have found. You would have to run your own. Right now for the short term, I have my electric choke tapped into the blower motor. This is on the ignition circuit if I remember correctly. I turn on the blower on high for a few minutes until the engine is warm and then use as needed.

They are designed to have 12V on them all the time with the ignition.

 

Here you go-

Best to run a wire to your fuse box.

Richard

choke wire by Richard Hayes, on Flickr

 

Does the electricity really run through the bimetallic element? I assumed (I don't think I've ever had a car with an electric choke) that the juice ran through a resistance element (tungsten? nichrome? something else?) which then heats up, and the heat from it causes the bimetallic element to to bend or uncoil, which opens the choke. Or IS the bimetallic element the resistance element?

Just trying to learn here.

Steve

 

I used the yellow wire to the wiper motor for power. Spliced it with a connector from advanced auto, kind of a "T" that folds over to make the connection, it works well! My understanding is you want it hot with ignition on, but not with accessories switch etc.

 

Dave,

I asked pretty much the same question a while back, purely out of academic interest. I can't find the thread, but working from memory,
generally, yes, the electric choke needs to remain energized to stay open. That seems to me like a waste of electricity, but I'm sure the load is so small that any cost in performance or efficiency is smaller than microscopic. Certainly for the kind of carb you are talking about, which I assume is aftermarket, the choke needs electricity to stay open. In the answer I was given, it was mentioned that there have been some OEM designs, including if I remember correctly, some C3 Corvettes, which are able keep the choke open using the heat of the engine and therefore turn the choke's electricity off once the engine is warmed up.



Steve

Steve

 

Not sure if there's an additional resistive element, or if the bimetallic element itself has a resistive component.

 

Thanks all. It looks like I will be finding an ignition-on power source and not putting it on a separate switch. I kind of have the same attitude that Steve has in that I don't like to have things energized if I don't need them. But it is what it is at this point. I like the fuse box idea. I have switched from an original Q-Jet and stock manifold to a Quick-Fuel Carb and Edelbrock intake. The new intake does not have a heat pot for the choke. Thanks Again.
Dave.

 

To answer your question, Yes. The coil is the bimetallic element and it is resistive. As it heats up, it gets more resistive and this is what keeps it from overheating and melting.

 

I thought about that a couple of time, but on mine, it's hot all the time. '68 coupe.

 

When I had Lars rebuild my QJ I had him change from hot air to electric choke. He also recommended splicing into wiper motor power which is constant power w/ignition on. Its close prox. simple and works great.

 

 

You can tap into the hot wire on the windshield wiper motor. It energizes after you turn on the key. It should be the terminal nearest the steering column. Saves on Wiring, I've done 8 of them tis way with no issues.

The power needs to stay on all the time. They really don't take much amperage.

You can snake the wire along the top of the motor and just tap in. You can even use a double plug so you don't have to cut a wire.

 

Thanks again all. Good ideas. The wiper motor looks like an option too. Pressure sw would be a good idea too, but I have a oil line to mechanical gauge. But now I have the theory down I'll decide about which way to go soon. Thanks again. Dave.

 

Another vote for the wiper motor +12v. wire........works perfectly.

 

There are two places to install a GM style oil pressure switch for the choke. The rear of the intake is obvious but there is also a pressurized threaded port just above the oil filter pad. There should be an ignition hot lead available in your firewall bulkhead connector....usually, GM used a 16 ga pink w/blk stripe to one side of the oil switch, then the other terminal had two leads coming off it-one is dark blue (goes back to the firewall bulkhead for the choke light) and a light blue that routes out to the electric choke on the carb. I like to keep a factory appearance so yet another option for ya!

 

So this is how GM powered the electric chokes from the factory?

 

I just did this with my new Edelbrock carb and it worked perfectly, and easy to get to.