As I stated in a previous thread, I just got my Olds back from having the engine rebuilt. Today I was under the hood checking some things and I noticed nothing is hooked into my Vacuum Switch anymore. The hoses that used to go though it have been re-routed. I believe that he did this because the Q-Jet was replaced with a new Edelbrock Performer (long story). Before I call him with a "What the He#$!" conversation, I'm just trying to figure out if I need to.

I know the switch is there to advance the timing because of the a/c. Will I run into issues if I run the a/c without it? It's not connected via the top clip. Should I just cap the 4 ports and call it even?

 

You are incorrect about the switch operation.
It is an early emissions control device that restricts vacuum advance timing until the engine is up to operating temperature and the transmission is in high (third) gear, which reduces tailpipe emissions.

Most people who are not looking for 100% concourse correct show car setup bypass it and connect either ported vacuum or full manifold vacuum to the distributor advance can for better driveability, performance, and economy.

 

OK. Thanks. That is what he set up. Do you think that I should cap them? Or doesn't it matter.

 

The switch gets its vacuum from a hose connected to the intake manifold, so if that is not connected there is no vacuum source, so no need to cap the ports.

 

I would pull the unit and replace it with a pipe plug.

 

If you use it and follow the factory tune-up procedure, your engine will be less stinky at idle. That, and the correctness factor would be the two reasons a person would hook it up. Otherwise, your engine will run fine without it. In that case you would follow Kenneth's advice on timing.

There's no problem hooking it to a different carb, you just have to look up which ports have which function.

 

To clarify a little: Transmission Controlled Spark was an early attempt to control NOx emissions. It did this by preventing vacuum advance in lower gears. The thermal vacuum switch actually has two purposes. The electrical terminals on top connect to the transmission switch that shuts off vacuum to the distributor unless the trans is in high gear. This is a normally open valve, so if the wires are not connected, you get vacuum at all times, disabling the TCS function. Of course, with no other hoses connected to the valve, it isn't functioning anyway.

The other function of the valve is to prevent overheating at idle. From the factory this car used ported vacuum to operate distributor vacuum advance. Ported vacuum provides no advance at idle. Under high temp low speed conditions, if the car starts to overheat, this thermal vacuum switch is designed to switch the vacuum advance from ported to full manifold vacuum. This advances the timing at idle, which increases engine speed and improves cooling. Again, without the valve connected, this function is disabled.

Unfortunately, with the aftermarket carb, we have no idea how your vacuum advance is currently set up. The E-brock has both ported and manifold vacuum ports - which one is operating the distributor advance can? More to the point, it isn't always the right thing to use straight manifold vacuum. The original distributor has an advance curve that was designed assuming ported vacuum. Using straight manifold vacuum could either cause pinging at midrange due to excessive advance (if the initial timing is set to spec) or inadequate timing at full throttle if the initial is retarded to prevent this pinging. Of course, the factory advance curve assumed early 1970s gasoline and a totally stock engine. The only certainty is that the factory timing and advance curve isn't optimum for today.