Electric choke power source

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BJedi76

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I have an 86’ 4x4 GMC Sierra Classic 1500 swb 305” 700R4

I have an old carburetor and I’m changing the thermostatic choke to electric. what is the best source for the power?

thank you…
 
AuroraGirl

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BJedi76 said:
I have an 86’ 4x4 GMC Sierra Classic 1500 swb 305” 700R4

I have an old carburetor and I’m changing the thermostatic choke to electric. what is the best source for the power?

thank you…
Click to expand...
I have currently key-on ignition power and it works, however, from what I gather, if you leave the key on you will open up the choke too much, causing it to be hard to start. Apparently the oil pressure bypass switch will give keyed ignition when the truck is RUNNING versus when the key is on, preventing the choke from heating up while the truck is off.
 
chengny

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Yeah, the oil pressure switch performs two functions.

1. At start-up it is designed to apply battery voltage to the choke heater coil as soon as the engine is running. There may be a momentary lag - until oil pressure is established (around 10 psi).

2. When the engine is shut off (and oil pressure drops to 0 psi), the switch opens and power to the heater coil is secured. This is helpful because, if for some reason, the ignition switch needs to be left in the RUN position while the engine is off, the choke heater won't restrict the closing motion of the plates.


If your engine still has the oil pressure switch (two terminals) and the oil pressure sender (single terminal) run a keyed power source to one side of the switch. The sender (bell shaped) is for gauge operation only and is unrelated to the choke heater circuit:

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Also run a lead from the other terminal over to your carb's choke heater. The image below shows that lead connected to a Q-jet. Q-jets are self grounding through the carburetor housing so no ground lead is needed, but some after market carbs will require an external ground wire:

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AuroraGirl

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chengny said:
Yeah, the oil pressure switch performs two functions.

1. At start-up it is designed to apply battery voltage to the choke heater coil as soon as the engine is running. There may be a momentary lag - until oil pressure is established (around 10 psi).

2. When the engine is shut off (and oil pressure drops to 0 psi), the switch opens and power to the heater coil is secured. This is helpful because, if for some reason, the ignition switch needs to be left in the RUN position while the engine is off, the choke heater won't restrict the closing motion of the plates.


If your engine still has the oil pressure switch (two terminals) and the oil pressure sender (single terminal) run a keyed power source to one side of the switch. The sender (bell shaped) is for gauge operation only and is unrelated to the choke heater circuit:

You must be registered for see images attach


Also run a lead from the other terminal over to your carb's choke heater. The image below shows that lead connected to a Q-jet. Q-jets are self grounding through the carburetor housing so no ground lead is needed, but some after market carbs will require an external ground wire:

You must be registered for see images attach
Click to expand...
Where does one get the block to put a second switch such as that in? I only have the single big one, for sending for the gauge. I would need the small one and the splice block for running it on mine.
 
chengny

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AuroraGirl said:
Where does one get the block to put a second switch such as that in? I only have the single big one, for sending for the gauge. I would need the small one and the splice block for running it on mine.
Click to expand...

At this point...you'd probably only find one in a junkyard. I would suggest that you don't try to make your own out of pipe fittings. I have tried several times before and the end result always has one problem or another (usually it's too big).
 
75gmck25

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Summit racing and Jegs sell brass T’s for pressure gauges, and they used to stock them in Autozone and Advance Auto near the gauges. I’ve never used one, but they are easy to find.

Bruce
 
Havasublue

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Whatever you do...
Make sure it is completely isolated from the ignition. Electrical power keeps the choke open.
It will close for starting by itself. I ran a switched hot wire. When the truck starts...power the choke.
 
Havasublue

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Make sure of where you get power for the choke!
It can drain your battery overnight!
Rob your ignition of power...
Weak spark, fouled plugs, hardstarting, etc.
 
Turbo4whl

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AuroraGirl said:
Where does one get the block to put a second switch such as that in? I only have the single big one, for sending for the gauge. I would need the small one and the splice block for running it on mine.
Click to expand...

There are two places on the block to access oil pressure. The rear, top edge of the block, driver's side (common). This location is 1/8" pipe.

The second location, 1/4" pipe, near the oil filter. This location not always good for a sender or a pressure switch because the driver's side exhaust may be very close.
 
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