I've got roughly 350 miles on the new 427 in my 65 L78 Roadster and so far so good. The carb is an almost new Holley 770 Avenger with an electric choke.
I've noticed that no matter how I adjust the choke butterfly, the start up is always a bit ragged and that might be due to where I connected the chokes 12V power lead.
When I got the car back in late 2019, the wiring was a bit 'busy' and had a CD ignition setup along with a few other things that I removed.
After 5 years of work on this roadster, I was about ready to fire up the new Bigblock but wasn't sure where the 12V power lead had been hooked up to before I started this project
so I wired it to the incoming power side of the ballast resistor (original L78 TI setup long gone as was the original 396).
After doing a little research, I found that my choice of power source might have been a mistake as the electric choke can draw quite a lot and the general consensus is to never connect
it to the ignition system because it can compromise the strength of the spark reaching the plugs. Two of my midyears still use the divorced mechanical choke and work well.
The other Midyear, my 65 smallblock has an electric choke on the Edelbrock Performer carb
and it works well with no hiccups but it derives power from the Brown Wire that supplies power to the windshield washer setup.
Had that car for 40 years and suspect I might have done the 'add-on' wiring for the electric choke before the engine went back in. The 65 L78 is now up and running and that Brown Wire on the wiper motor
has hardly any slack in it to be able to solder in an additional lead so looking for suggestions on a 12V lead that's only powered up when the key is on.
I read some folks like to use the fuse block as their source but in my case, I have Power Windows (and I added the 4-way 66 flasher setup as well) so both those leads are hot all the time, not just when the key is on.
One other potential power source that might work but has drawbacks is the factory Backup Light connector at the engine side of the firewall. My 65 must have had Backups when it was new but along the way, that got
changed and I have 4 red taillights at the back end, no backups anymore. That connector has a Pink Wire lead that is keyed but...it's only an 18-gauge wire while the Brown Wire at the Wiper is 16 gauge.
I happen to have the Holley Electric Choke kit and the instructions in it say to use a 10A fuse for the power lead. That seems a bit high if I use the 18-gauge Backup connector to power up the electric choke...or so it seems to me.
So, I'm looking for a Keyed 12V power source that won't have me removing half the engine to get to for the splicing.
Thanks,
Mike T - Prescott AZ

 

I would use a Bosch style relay to power the choke. Either a 4 or 5 pin unit, have used them many times to power such things as convertible top motor, radiator fans, head lights and more. Contact me if you want more info.
Joe

 

My `65 had an unused fitting (V or L shaped, depending on how you looked at it) on the firewall behind and above the distributor. One side was switched (ignition) 12V. It looked factory but I never knew what it was for but it worked perfectly for an electric choke.

 

Mike,

Taking power for the electric choke from the hot side of the ballast resistor is the right way to do it. That's how the electric "chokes" on ALL Rochester FI units with electric heated "chokes" get power.

If you need to feel more comfortable about making that connection, measure the current drawn by the choke heating element. If it's in the range of 1A - 2A, you are good to go. For reference, FI "choke" heaters draw a little over 1A.

Good luck,

Jim

 

Joe - I appreciate the offer, I just sent a PM.
VetteRodder - That's the 'L' connector I was describing that had been originally for the Backup Light setup but mine having been converted (to no backup lights) leaves it available but since it's only 18-gauge wiring, I am a bit hesitant to use it with a 10A fuse as Holley suggests.
Jim - Did not know that. Here I was thinking my very rough initial idle routine was due to me using the Ballast Resistor as my power source and the choke coil tapping off a bit too much 'juice' and compromising the spark strength.
I did do some rummaging around to see what other folks had been using and do completely understand that some of the info I'm reading may be sketchy or may be good to go but as to amp draw on a choke, here's a slice of what I had
been reading about and gave me pause to rethink my source for the electric choke.

I use 16 gauge whenever I wire up an electric choke.
Out of curiosity, I just tested the current draw on an electric choke I had sitting around. For the first 1/4 second, it spiked at 6.5 amps and dropped to 1.3 amps. After that, as the coil heats up, it steadily dropped from 1.3 and leveled out at about .75 amps. So that explains the need for a 10A fuse when the device only draws an average of less than an amp.

The initial draw is more than I had expected but knowing Holley recommends a 10A fuse on the power wire to the choke, that sounded reasonable. Even later on, as the choke heats up and the draw diminishes, there's still a tap-off of power...or so it seems to me.

Mike T - Prescott AZ

 

OK, yes, the heating element draws power but the wire which supplies power to the ballast resistor is more than up to the task of supplying power to ignition and electric heater.

Here is how to convince yourself of that:

- With the engine running and the heater DISCONNECTED, measure the Voltage at the hot side of the ballast resistor.

- Now, connect the heater, and with the engine again running, again measure the Voltage at the hot side of the ballast resistor.

I predict the two readings will be within ~0.1 Volt of each other and if so, there is no issue.

 

I have been using relays more and more on my old cars. The amperage draw on the signal side is very minimal and almost undetectable. The thing to remember is to add a fuse to protect the wire and device on the load side which is generally fed from the battery. Just a note

 

Jim - I did a little testing but just realized I didn't follow your instructions correctly. The battery indicates 12.54 volts. Then, with the engine OFF and with the choke lead hooked up at the Ballast Resistor
I measured only 11.28 volts at the Ballast Resistor. Disconnected the choke lead from that end of the Ballast Resistor and still it read the same...11.28 volts.
I ran across an older thread where Lars had recommended running a wire from the (-) side of the coil to ground when checking for voltage but that doesn't seem to have made a difference.
Here's what Lars wrote: You can take a jumper wire (with alligator clips) and run it from the "-" side of the coil directly to ground. Then turn the ignition switch on and check the voltage on either side of the ballast. In this coniguration, one side will read battery voltage, and the other side (coil side) will read a reduced voltage from the volatge drop through the ballast. The ballast will get hot, so don't touch it.
I know you mentioned the engine should be running but I was still expecting to see battery voltage at the ballast resistor. I'm doing something wrong here, just not sure what that is.
Mike T - Prescott AZ

 

The input side of the ballast resistor will work fine, as will the pink wire at the reverse light connector. You're way overthinking it, battery voltage is available at both and the choke will draw very little current. I won't use an electric choke on my cars, but if you intend to, those two OR the brown wire off the wiper connector will do the same. The ballast resistor will read the same voltage on both sides anytime the car is not running, unless the points happened to have stopped in the closed position when you turn it off. A resistor only drops voltage when current is passing through it. Points open, no current, no voltage drop.

 

Yeah, I have a tendency to do that, overthink things and it sounds like there is no smoking gun here by wiring the electric choke on the Holley 770 to the input side of the ballast resistor.
For the helluvit, I just went out and disconnected the red power wire from the ballast resistor and checked to see what voltage it was showing when the battery was connected and
the ignition switch on and found 12.04 volts. The battery voltage when checked at the battery showed 12.54 so the half-volt drop is just normal wiring resistance?
Thanks.
Mike T - Prescott AZ

 

I've used the wiper wire before also on other cars -non Vettes.

 

@65GGvert, Why won’t you use an electric choke on your cars? Is there a technical issue or just preserving originality?
I’m in the process of installing a Holley with electric choke on my 67 and it will be my first experience so I’m concerned that I may have problems with it.

 

I don't like 12 V wires, running around the engine and always having power on them, even when the engine is not running. I also don't like that if the switch is turned on for some reason, the choke heats up and starts off before the temperature of the carburetor does. I want the choke to go off when the engine warms up, not when the choke element warms up. The original look is also a factor for me.

 

Soon after I bought it:


After changing the choke:




Final after engine clean up:

 

65GGvert, Those all sound like valid concerns. I bought a separate temp sender wire with sheath to use for the power connection but am trying to figure out the best and least conspicuous way to add an inline fuse for the reasons you pointed out.
Biggest remaining concern is how to make an electric heater simulate engine warmup, especially since I have blocked the exhaust crossover to minimize carb heating and percolation.

 

Millions of people use them, particularly with aftermarket carbs and they work. About the same warmup as mechanical as long as you adjust properly and start the car soon after key on in cold weather. I just don't like them for the reasons I outlined.

 

I have an electric choke on 1 car when I agreed with myself to replace a OEM Motocraft 4100 with a Holley. It works.
However the mechanical choke with heat tube or stove are responsive to actual engine temperature rather than the arbitrary heat made from a nichrome wire. In the end it comes out close, but a properly adjusted mechanical choke reading engine temperature is a better way to go IF you can get there easily enough. For unmodified cars OEM carburettors are best, in my opinion.

Keep your (old) GM car all (old) GM!

Dan

 

I found that with an electric choke on a Holley, the car would start well when the engine was cold, and the engine would fast idle to about 1400 RPM. The fast idle RPM would begin to reduce as the the engine AND the electric choke warmed up. The problem I experienced was when I stopped the car for 10 minutes or so and restarted the already warm engine, the electric choke had cooled off and reset the fast idle. As the engine was still warm it did not need the 1400 RPM the fast idle that was imposing on it. I tried many different adjustments but the rate of choke cool down compared to engine cool down was never the same. I know why some prefer the exhaust manifold heated choke of factory designed system.
Having said all this, the electric choke on my Rochester FI does not suffer this problem... Al

 

Figure GM used electric chokes on all the cars/trucks into the late 70s-80s until they went EFI.