Customs Vacuum hook up

Putting a Quick Fuel Slayer 4 barrel carb on a big block Ford custom I am doing and I see I have 2 vacuum ports on the front right side of this carb. Which port do I hook my distributor vacuum to? Pic of carb and front plugged now … ports attached.

 

The one to the left of fuel level sight glass.

 

Do you know what kind of vacuum is supplied by each port? (I would think one is for straight manifold vacuum and the other is for ported vacuum.) The rule of thumb is ported vacuum for optimum emissions and manifold vacuum for optimum performance; take your pick. It should be in the paperwork you got with the carb.

 

I had thought this thread was headed in a totally different direction...

 

Unfortunately no paper work .

 

Either port should work to get your rod running.
Do you have a vacuum gauge?
If so, attach it to each port at idle, while the unused port is plugged.
One of the ports (manifold vacuum) should have a reading at idle.
The other port (ported vacuum) should not draw vacuum at idle.

I'd suggest using manifold vacuum for a street driven rod.

 

You’ve got 3 vac sources in that pic

the one on the metering block is ported

the outside one on the throttle plate is manifold

the inside one on the throttle plate I think is ported.

if you turn the carb over you can see the drillings on the throttle plate one will come out under the butterfly one won’t.

 

No differant than a Holley.

 

Which ever one makes the engine idle the best. Some like full vacuum, some don't, depends on the engine configuration. At full throttle it doesn't matter.

 

As others have said, one is manifold and the other is ported. Whoever is going to tune the engine will have to decide which one to use.

 

Try both ways. I tried manifold on my 455 and it didn't sound happy, went back to ported.

 

Ford OHV V-8's from '57 on generally used ported vacuum for years, even before the emissions issue reared its head.

Try both and see which one it likes best...