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Distributor vacuum control valve

N

Neglected68

Member
When I bought my car, a PO had replaced the stock distributor vacuum control valve with what looks to be an electrical version. It is wired to the coil, and has one vacuum line running from the intake manifold vacuum port and the other to the distributor. Has anyone ever seen this before? I am going to install my new Stealth intake and Summit 4bbl carb soon, so I am wondering if I should reinstall this vacuum control valve (I have no idea if it even works) or go back to the original type. Any opinions?
 
That's an electric vacuum switching valve. Basically, an on/off switch for vacuum.

Where do the wires go from the valve?

It's running on manifold vacuum also. Is there only one vacuum line to the distributor?
 
There are two vac lines to the distributor. The line from the switch runs to the intake vacuum port, and there is a line from the carb to the carb vac port. I pushed the spark plug wires out of the way in hopes of getting a less confusing shot in the picture below.

The wire with the red connector goes to the pos side of the coil; the one with the blue connector gets bundled up with the wire from the water temp sending unit and a wire from the coil, then goes to through the firewall via the larger red plug in the second pic.
 
At one point in time, California required cars brought into the state that didn't have factory CA emissions to use a variety of aftermarket emissions reduction retrofit gadgets. If your car came from one of the other 49, I would suspect this is one of those gizzmos.
 
"1497" said:
At one point in time, California required cars brought into the state that didn't have factory CA emissions to use a variety of aftermarket emissions reduction retrofit gadgets. If your car came from one of the other 49, I would suspect this is one of those gizzmos.
Click to expand...

I hadn't thought about that - I was assuming it was some cheapo mod supposedly for more power. My car was built in San Jose and sold in San Diego. I think it spent most of its first two decades in that area. I bought it in '88 in Escondido (northern San Diego County.) But that doesn't mean it wasn't a mod for the smog certifications, since it did need to pass smog for most of the years it was on the road.
 
Hmmm....

Is the wire with the blue connector spliced into the coolant temp wire? If so it is some kind of attempt to retard the timing when the temp is high enough to cause a ground.
 
I mis-typed - the wire from the blue connector isn't spliced, just running next to the other wires in the plastic wrap that protects the wires as they run through the engine compartment. I know there is a technical name for that, but I can't remember it now.
 
I can't tell where the wires go once they are through the firewall. The wiring schematics in '68 shop manual are not much help. One of the wires goes to the temperature guage. Could the wire from the vacuum switch go to the ingition switch or a ground? Seems odd to me to run to something in the interior of the car.

Electical systems are so not my strength. I know not to stick a fork in the wall socket, but that's about all.
 
From looking at it and reading your description, it appears to be a electo-magnetic vacuum switching valve. One side is wired to the positive side of the coil (constant power with key on) so the switch is activated by supplying ground to the other wire.

I am not completely sure, but I think these switches came out in the mid 80s or later. Most vacuum switches prior to that were of the thermo variety. (remember the ones that screwed in the manifold and broke off after a few years.

I doubt that it is factory installed. I could be wrong though.

Whatever it is, wherever it came from, it's job seems to be to retard and/or prevent timing advance.
 
I am tempted to replace the switch with the original thermally activated switch. Perhaps I should wait until after I get the new manifold and carb on and the car running. It would be smarter to change one thing at a time...
 
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