Vacuum Ports Where Do They Go?

[worms442]

The Car
1986 Oldsmobile Cutlass 442

I have a question about my carburetor vacuum ports. I dont have an original carburetor, Its 4 Barrel, and has 4 vacuum ports two which have vacuum at idle and open throttle, the other two have no vacuum until you accelerate.
I was wondering what hoses go connected to these ports.

My car is off the computer and EGR is capped off.
I have a Vacuum Advance Distributor so that takes care of one of four ports, I also have my heater/ac vents hooked up to the other vacuum port that always has vacuum.

So now I have two ports that have no vacuum at idle but only on acceleration. What can I use these two ports for or should I cap them off.

Also,
Is the Distributor hooked up to the right vacuum port?
I read some other threads do Power Brakes have a hose thats supposed to be hooked up to a Vacuum Port is this true?
All info and suggestions welcome.

 

[mhamilton]

Well, the a/c controls and brake booster get manifold vacuum, but those (on stock cars) have their own connections to the intake.

The non-computer EGR valve and HEI advance get ported vacuum (above throttle plates, no vac at idle) in stock configurations. Any unused ports should be capped off. You can put the vacuum advance to manifold vacuum, see whichever works better for you. GM changed that around over the years. But if it's a stock HEI and carb, then ported vac.

Hope this helps,
-Michael

 

[patmckinneyracing]

First thing is YES, there should be a hose running from your power booster that goes on the big vacuum port on the back of the carb. Second, there should be a large port in between the two small ones in the front of the carb. Your supposed to run a hose from your valve cover and put it on that large port in front. Third, you want to hook up the hose coming from your distributor to the port on the left (when your staring at the motor from the front of the car) which should be the one that gives vacuum on acceleration. The reason behind this is because if you hook up that hose to the port providing constant vacuum, then your car's timing is sitting too high for driving around town and is basically useless. The only time you want to switch to the constant vacuum port is if your fixing to do some sort of racing. So make sure you cap off the constant vacuum port.

PS The way you tell which one is constant vacuum is by uncapping both of those small ports and using your finger to plug one of them. Listen and see if you hear a constant whistling sound. If your here that, then you found out which one is the constant vacuum port and vice versa. BTW what brand of carb are you running? My description is meant for an edelbrock type or similar.

 

[foxtrot]

> HEI advance get ported vacuum (above throttle plates, no vac at idle)

On a non-CCC auto the hie vacuum port is connoected to constant vacuum and NOT ported vacuum.

Here is a good read that explains this:
http://rockridgefarm.com/vettdoc/Timing_101.pdf

 

[mhamilton]

On a non-CCC auto the hie vacuum port is connoected to constant vacuum and NOT ported vacuum.

Here is a good read that explains this:
http://rockridgefarm.com/vettdoc/Timing_101.pdf

That article is very good, but on cars from this era the factory setup was to connect the vacuum advance to ported vacuum. In fact, some of these models just before the 1981 switch to CCC, used a modulator valve to mix both ported and manifold vacuum (the 200 and 229 V6, for example).

 

[worms442]

Ok, Thanks for advice!
My distributor is on constant vacuum so tomorrow im going to set it on a port that gets vacuum on acceleration.
Im gonna reset the timing to 20 and re-adjust idle/mixture with new timing.
Im guessing my ac/heater lines are on the right port constant vacuum.

As for the Brake Booster hose should it be connected to constant carb vacuum? What difference does this hose being connected or disconnected make?

I will check what carb it is, its from autozone so ill look it up tomorrow morning.

 

[patmckinneyracing]

I have no clue of why you think your AC or heater hose would be hooked up to the vacuum on the carb. The power booster hose needs to be hooked up to the back vacuum port on the carb. This is what gives you powered brakes. If you don't have this set up, they you won't have brakes because your car is not designed for manual brakes. Do you have any pics of your carb?