1966 electric choke

[dgll411]

hello, I am now working on the electric choke which was installed years ago by a previous owner. I discovered that there is constant 12 volts at the + connection with the ignition off. With the key on there is about a 6 volt reading and a reading on the negative terminal. It looks like there is a relay that I suspect has gone bad. Is the relay necessary? I see videos of direct 12 volts to +  and ground the negative. Mine has a wire to the back of the alternator and a wire to the wiper motor. I guess to delay operation until the car is running. I would like to eliminate the relay if possible.
Secondly, Im wondering if the choke has gone bad from constant power supplied. If so, how can I test it and where can I get a new one? I am not seeing them in the parts store. Thanks to all

[TJ Hopland]

What sort of carb are we dealing with here?  The Rochester factory style electric chokes just had one wire and grounded through the body.  Since the Carter AFB went onto become the Edelbrock carb you can buy the electric choke kit for those anywhere that sells 'hot rod' parts and fairly easily make it work on an old AFB.  Those and many of the aftermarket kits had 2 terminals but usually one just gets a short jumper wire to a good ground.

Hard to tell what is going on from your description.  My best guess is they are operating the relay from a key on signal from the alternator and they are taking the constant +12 from the wipers always live park circuit assuming a 66 has one?  Or maybe the other way around they are getting the +12 from the battery terminal on the back of the alternator and the park circuit is only live with the key on?  Seems like there would be better ways to do it.

The relay is a good idea when you are adding things because you want to be careful you are not overloading the switched key circuit with the new device.  A don't know how much power a choke takes so maybe its not an issue but its usually safer to use a relay if you are not sure.  The other part of safe is where ever the +12 is coming from should be fused especially if its direct(ish) from the battery.

The way the GM factory did the electric chokes which for Cadillac started in 1975 was via the oil pressure switch.  The switches for the cars that had electric choke had 3 terminals.  One terminal was the usual closed to ground when the pressure was low.  The other 2 terminals were closed to each other when there was pressure.  The power to that was a key on circuit, not sure which.  Thats why the oil light also said choke on it. 

They did that so if you turned the key on for some reason but didn't start the engine the choke would not start to unwind and cause a hard start.  Now days the switches are often sold as a fuel pump safety switch.  When GM went to EFI they used that pressure circuit to run the fuel pump after cranking.  The idea was if the fuel line was ruptured the engine would stall so the oil pressure would drop and the pump would then shut off and not be adding fuel to the possibly literal fire.  I think by the mid 90's the computer just watched the tach signal to know if it should run the fuel pump.    

[TJ Hopland]

Oh and to test it you could try an ohm meter between the terminals with the wire disconnected.  I would expect the ohm reading to be under 500 ohms.  You could also just see if the choke closes if you disconnect it and opens after a few minutes when it gets power.

They normally have power anytime the engine is running so they do spend a lot of time on so its possible its still working.


https://www.summitracing.com/parts/edl-1478

I think this is the kit that can be fairly easily modded to fit the AFB's so if you need a new coil maybe this can be the start of tracking one down.  I think most of the aftermarket and conversion kits use the same coil so I would not think it would be that hard to find one.

[dgll411]

Its  a Rochester 4gc I believe.  The choke is a napa part. Will any choke thermostat work or do I need a part number?  I'm guessing the spring is faulty. 

[Chopper1942]

It is very unusal for the thermostat spring to fail. Check the resistance of the choke heating element. If single wire, connect your DMM lead from the B+ terminal of the choke and the B- lead to the carb body. If the DMM reads O or OL, you do not have continuity between the B+ terminal and the element's ground.  If it has 2 terminals, connect the DMM between the 2 terminals.

I would run a wire from the fuse block to the choke terminal with a fuse installed in the wire.  Find a terminal that is only hot in the run position. Connect the fused wire to the hot side of the terminal. If there is an open fuse location in the fuse block that is hot in the run position, install a fuse and connect choke B+ wire to the fused sided.

If 2 teriminal choke, run the other wire to a known good ground and use a star washer between the wire terminal and the ground.

[dgll411]

Upon checking the resistance between the 2 terminals, the meter remained on 1. I also connected it to 12 volts off of the carb and the spring did not move. I think its junk.

[Chopper1942]

1 ohm sounds kind of low. The circuit would initially need 14-15 amps on startup.  Take a heat gun and put it on high and blow air on the spring. If the spring unwinds, it is probably OK.  Also, if the heater coil is working, the cover should get hot to the touch.

[TJ Hopland]

I'm assuming that is just what his meter reads with an open circuit.

There are a lot of variables in those choke coils.   I think its Ford that had a special terminal on the alternator with the idea being alternator won't be putting out unless the engine is turning and on those I'm pretty sure they will burn out if you send em straight system voltage of 14.

One conversion kit I remember working on kept burning up and I eventually found out that it still needed the vacuum port open that was there for the original air operated choke.

[dgll411]

Yes, 1 is an open circuit on this meter.

[TJ Hopland]

Are there any markings on the choke coil?  Inside or out?   

[dgll411]

Its a napa product