Can't find ported vacuum on carb # 7027210

[completeunknown]

I cannot seem to find a ported vacuum port on the carb that I am currently using, which is carb #7027210.  This shows to be a 1967 model carb.  Did the older carbs not have a ported vacuum port?  It is my understanding that the port on the driver's side front of the carb, above the primaries, should only have vacuum when the primaries are opened.  I thought that maybe the primaries were staying open a little bit so I turned the idle screw to where the engine would barely run.  There was still vacuum at that port.  What else do I need to look at the cure this problem?  The carb was rebuilt a few years ago by a local guy that is probably the most well known carb-man in this area.

Thanks

[73 Z28]

To determine if a fitting uses manifold or ported vacuum hook a vacuum gauge to the fitting and start the engine. Observe the vacuum with engine idling then rev engine and observe vacuum reading. Ported vacuum increases with an increase in RPM. Manifold vacuum drops off with an increase in engine RPM.

Good Luck!!

[completeunknown]

73 z28,
Thanks.  Just to clarify, you are saying that a ported vacuum port can still show vacuum at idle? 

[73 Z28]

Yes , what you are looking for with the vacuum gauge installed to different vacuum fittings on the carb is how the vacuum reads at idle and then while revving the engine. An increase in vacuum while revving the engine indicates a ported vacuum source and a decrease indicates a manifold source.  Once you've checked a few different vacuum fittings on your carb, you see exactly which one you need to use.

[completeunknown]

I had a chance this weekend to get the vacuum gauge out and check the carb again.  On every fitting that I tried, the vacuum would drop when I opened the throttle.  I could not find a port where the vacuum increased when opening the throttle.  Any other suggestions?

[73 Z28]

How many vacuum fittings does your carb have?   Some marine application carbs had only 1 or 2 and used no ported vacuum fittings.

[completeunknown]

It has one coming out the passenger side that looks to be above the primary butterflies, a big one coming out the front, a small one that the vacuum break is connected to, and one on the front driver's side that looks like it is above the primary butterflies.  I believe the one on the front driver's side should be ported vacuum, but according to the vacuum gauge none of the fittings are ported vacuum.

Thanks

[Cliff Ruggles]

Many early carburetors didn't provide a ported vacuum fitting for the distributor advance.  In and after 1968 most will have one, main casting, front, drivers side.....Cliff