Power Source For Electric Choke

[Nacho-RT74]

Ok, let's see...

Our cars are originally designed to get the choke operating with the engine temperature from the intake crossover. That's actually the CORRECT way to set the choke control since is the real temperature reference.

The electric choke source is a help to get the engine at low iddle cam position on carb cam a bit faster than just the engine temperature, helping to the bimetalic coil spring to get heat with the heating element ( resistor ). With the electric assist you can get your iddle speed in, lets say 3 or 4 minutes, instead 7 or 8 minutes. But engine temp is still working in it. Mixture was getting already warm on that time.

This is of course if you did't blocked the crossover provisions on heads.

If you have had your car already operating, engine already got warm allong the day. If you let the key in ACC afew minutes then start up the engine, won't affect anything, since the engine was already warm. The car will start up correctly at iddling with the choke down. No matter if choke was being sourced from the electric assistance. Engine is already warm from the regular operation and will iddle nicelly.

Now, if engine is cold from overnight and you let the key in ACC for some time, the choke will be open due the heating element sourced from the electric assistance, and not from the engine temp. If this happens, the fast iddle cam on carb won't get in, so if you start up the engine, will iddle like you don't have choke, cold mixture, iddling erratically. Mostly sure will need to crank the engine several times, or giving throttle to keep the engine running untill get the operating temperature. Simply like you don't have choke.

This happens if you let the key in RUN too of course, but that's a default. As mentioned, this was corrected on later years with a oil sender with a built in switch, able to switch on the power just when sense the oil, so with engine running. With this sender, you can feed from the run circuit any device but just power on when engine is running, the choke for example.

 

[Nacho-RT74]

at the end everything will depend on the engine bay temp and enviroment, to get the engine nicelly iddling. The electric choke source is just an assistant to help a bit on get the choke down faster.

Are you using the electric choke control? Or just feeding the choke coil straight from the power source?

This is for /6 and SB ( single stage )

BB ( double stage ) units got this same unit with a ceramic ballast attached

 

[idrivemopar]

Thanks Natcho, always wondered why one of the controls I have had a ballast resistor on it. Now I know!

 

[Ranger16]

at the end everything will depend on the engine bay temp and enviroment, to get the engine nicelly iddling. The electric choke source is just an assistant to help a bit on get the choke down faster.

One of the first forms of emission control.

 

[72RoadrunnerGTX]

Should be noted that recent posted info here discusses the factory style electrically assisted divorced choke system first used for the ’73 model year. As mentioned, both intake manifold crossover heat and heat generated by the heating element is needed to have the system work as designed unlike aftermarket electric chokes that function independent of any other heat source. I took the question asked in the OP as a reference to an aftermarket installation of a carburetor equipped with a more modern electric choke system. Such a system is designed to operate with full +12volts applied for the duration of the full run cycle to keep the choke spring relaxed. The factory style choke control cannot be used in that case as they are designed to stop current flow (or reduce in the case of versions with a resistor bypass) to the factory divorced choke heating element after a few minutes of engine operation. Aftermarket choke spring heating elements pull considerably less current than the original style as well, ~500ma vs. close to 2 amps for the factory choke heater.

This high current was responsible for the early failure of the choke controls back in the day, burned internal contacts. The controls were considered a tune-up replacement part back in the day due to their short life span . A later (‘76ish and up) solid state design didn’t fare much better.

 

[Nacho-RT74]

Thanks Natcho, always wondered why one of the controls I have had a ballast resistor on it. Now I know!

The ceramic ballast attached adds a second stage of voltage to give the power to the heating element on BB setups. Can't recall the voltage and temps relation on every stage, but its on FSM.

 

[Nacho-RT74]

that will source it when key in ACC which is incorrect, must be just when car goes to be on ignition process. If you put the key in ACC for some time, then start up the engine, the choke will be opened incorrectly.

actually the same happens when you set the key in RUN without crank it up, but I think you will barelly left the key in RUN to heard, let's say the Radio

this was corrected on even later cars, getting a switch built into the oil sender, just providing the RUN circuit source to the choke if engine is running

those senders/switchs are available around

quoting myself because had a mistake on my original post... corrected in Bold

 

[Nacho-RT74]

old diagram... pretty much basic... how it was wired the RUN circuit

 

[71charger_fan]

I have an extra female pigtail on my engine wiring harness. It's a blue wire coming off an alternator field terminal. There's no such wire in the diagram in the '71 service manual. So, I looked in the diagrams in a '74 FSM I have and it looks to me that it's an electric choke power lead. The shop that worked on my car wired the electric choke to the positive side of the coil. I'm going to switch my electric choke power from the coil to this unused pigtail.

 

[71charger_fan]

I had purchased a tach harness but never used it. I was able to use part of it to wire my electric choke as it had the proper plug molded onto it.

 

[Nacho-RT74]

I have an extra female pigtail on my engine wiring harness. It's a blue wire coming off an alternator field terminal. There's no such wire in the diagram in the '71 service manual. So, I looked in the diagrams in a '74 FSM I have and it looks to me that it's an electric choke power lead. The shop that worked on my car wired the electric choke to the positive side of the coil. I'm going to switch my electric choke power from the coil to this unused pigtail.

That's the use for that female plug, just right made for the choke

 

[Dan The Man]

I used the 12v side of my ballast resistor, and used a single male to double male piggyback splitter like this one. No cutting or splicing.View attachment 379108

I guess I would have to use 2 on a 4 prong ballast.