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Old 02-25-2011, 08:48 AM
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electric choke

I'm installing a summitt 600 cfm carb w/electric choke on my 56 chevy, which has a chevy 307 out of a 69 camaro in it. The instructions are not very specific about where to connect the wire for the electric choke? Old holley carb had a manual choke.

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Old 02-25-2011, 08:56 AM
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choke wire

use a switched hot and plug it on the terminal on the choke
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Old 02-25-2011, 10:56 AM
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This question must come up monthly, so I figured it was finally time to write a little tech article. Many folks use the wiper power feed, but this has problems. Simply using a switched power source, especially one that is hot in the ACC position, will cause the choke to open prematurely if the key is on but the engine is not running. Also, the combination of the always-on choke heater and the wiper load may blow the fuse.

GM used two different methods to power the choke, depending on the vehicle. Most used an oil pressure switch in the power line to the choke. This way, the choke doesn't start to heat up until the engine is running and there is oil pressure. On my 62 F-85, I ran a fused wire (20 A fuse) from the BATT terminal on the alternator to the switch, and from the switch to the choke. Very simple to wire and very clean. I like to use the Standard P/N PS64 switch. The middle terminal works the OIL light, the other two are a normally open switch that closes with oil pressure. Use these to control the choke. If you have an oil pressure gauge instead of a light, simply use a brass tee fitting to connect both this switch and your oil pressure sender.

Here's the sender:



Here's the wiring diagram:



The other way is to use a relay that is triggered by the field wire on the alternator (brown #1 wire on SI-family alternators, for example). The field wire is only hot when the alternator is turning. This is how GM wired the stock G-body cars with electric choke when the gauge package was installed. Of course the down side with that is that the choke will close if you break the alternator belt. A typical wiring diagram for the second method is here:

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Old 02-26-2011, 03:00 PM
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Nice job Joe, great examples . I use the relay method and power it from the alternator field wire. That way the only time the electric choke is being heated is when the engine is running. Of course coming off the oil pressure switch will accomplish the same thing.

Vince
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Old 02-26-2011, 04:21 PM
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Quote:
Originally Posted by joe_padavano
....Here's the wiring diagram:

With all due respect, Mr. Padavano, wouldn't this setup make the oil light glow constantly whenever the engine isn't running, even when the ignition is turned off?

Or is the oil light only grounding through the switch rather than getting power from there.
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Old 02-26-2011, 04:46 PM
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Quote:
Originally Posted by Joe G
With all due respect, Mr. Padavano, wouldn't this setup make the oil light glow constantly whenever the engine isn't running, even when the ignition is turned off?

Or is the oil light only grounding through the switch rather than getting power from there.
The oil light in GM cars grounds through the sender. The center terminal is electrically completely separate from the other two on the sender that I've shown. That's the whole reason for using the PS64 sender.
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Old 02-26-2011, 05:21 PM
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Is a 20A fuse a little large for a choke heater? I use a 3 amp fuse in my Holley choke heater circuit.
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Old 02-26-2011, 05:37 PM
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Quote:
Originally Posted by DanielC
Is a 20A fuse a little large for a choke heater? I use a 3 amp fuse in my Holley choke heater circuit.
GM used a 20A fuse and appropriately sized wire gauge for their factory-installed electric chokes. I used the same.

Edit:

The choke is only load on that circuit, so it's not like the 20A circuit is powering other loads, either.
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Old 02-27-2011, 08:05 AM
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A 20a fuse IMHO is a bit overkill, but not if the wire it's protecting is proplerly sized which is a #12 AWG. My electric choke on my 34 is fued with a 5a fuse.

Vince
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