I need to know exactly where to hook up my 12v source wire I know I can ground straight to the carb but what is the best place to hook up? I have a 1980 chevy and trying the old rochester that's on it is crap!
This question must come up monthly. Simply using a switched power source, especially one that is hot in the ACC position, can cause the choke to open prematurely if the key is on but the engine is not running.
GM used two different methods, 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. 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.
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. 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:
What is that grey square thing that the 20A fused wire is running to on the 2nd diagram. I have a mechanical oil pressure so I don't think the first idea will work???
What is that grey square thing that the 20A fused wire is running to on the 2nd diagram. I have a mechanical oil pressure so I don't think the first idea will work???
That's the electrical representation of a relay, available at any auto parts store.
Of course, if you want to use the oil pressure switch, simply plumb a tee into the hole on the block. It's 1/8" NPT and you can get a nipple and tee at any hardware store. Then screw the switch into one side of the tee and the pressure gauge line into the other. GM did this on the Chevy pickups with gauges.
I just hooked up an electric choke on my holley carb and I love the thing. Starts up way better then using a manual choke. I ran mine like stated above off of my alternator of the one wire that normally goes to a voltage gauge or what ever else you use it on. What's nice about doing it that way it wont come on till engine is running. Electric chokes are the way to go for me. I only had to set my fast idle speed and nothing else.
Eric
Having started driving well before automatic chokes were used, I learned how to use the manual chokes with great success. When automatic chokes came along, went thru a learning process. The early auto chokes were not electric and you had to mash the accelerator to the floor to set the choke. This action also activated the accelerator pump, delivering a shot of raw fuel to the venturi. Both actions were key to cold starts since a richer fuel mixture is required. Carbs were designed to change the length of the pump setting and normally had 3 holes to make adjustments. Changing the adjustment from summer to winter and back to summer again was standard practice for near trouble free operation. As improvements were made in choke design, the accelerator pump stroke adjustment graduated to bending the connecting rod to increase or decrease the stroke. Coupled in the design of the auto chokes was the fast idle stepper cam and we all learned to tap the accelerator to step the idle down as the motor warmed up. The upgrade(?) to the electric choke took more learning and understanding of how this choke worked. Basically, turning the ignition on started heating up a resistor coil that lasted for about 90sec max, depending upon the starting temp of the choke housing. On extremely cold starts, failure to activate the start sequence immediately could lead to perceived choke problems. Further developments made these systems more foolproof for the mechanically retarded operators. All of this rant is based upon a well maintained carb which includes properly lubed and adjusted linkage. Worn and improperly adjusted linkage probably makes up the bulk of choke malfunctions.
Basically, manual chokes are bullet proof as long as the user understands the need to ensure a shot or two of accelerator pump action is required in extreme cold conditions and making the seasonal mechanical pump linkage adjustments.
Just another reason I use EFI on every thing I build.
Trees
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