4ADT manifold vacuum ports

[Grantbradley]

Hello . First a big ThankYou to everyone in helping me with mt 4adt restoration over the years. I am finally ready
to get the car on the road soon and i very much appreciate the help .
Now my question today is the original use of the two brass vacuum ports on the intake manifold,one for each
Carb. Were these for the dist. advance ? If so why two?
Grant

[Phillip]

Hey Grant,

These are actually the fuel overflow drains in case the engine gets flooded. There should be two thin drain tubes coming out of the center of those brass nuts. They are either steel or copper. I've seen both used.

If you have a real 4AD-T; i.e; a 4AD that came from the factory with twin carbs, you'll also have a Lucas vacuum advance distributor rather than the standard type with mechanical advance. There should be a vacuum port on the manifold for that.

Hope that helps!

[Phillip]

Hey Grant,

Here are some photos to help you out...

These are the overflow pipes that come out of the manifold below each carb:

Overflow Pipes_WEB.jpg (353.01 KiB) Viewed 4287 times

The vacuum line for the distributor runs from a tapped tube on the second carb and runs around the back of the block:

Vacuum line from carb_WEB.jpg (286.87 KiB) Viewed 4287 times

It then comes round the other side and ends up in the distributor vacuum advance unit:

Vacuum line to Distributor_WEB.jpg (367.81 KiB) Viewed 4287 times

Hope that helps!

Cheers,
Phlllip

[mikeyr]

the overflow pipes on the picture above are much too large in diameter and too long. The originals were 1/8" pipe pinched at the end to allow fuel to leak but minimize the vacuum loss. They were about 5-6" long also.

You can hook up your distributor advance to either one of those but you will lose the overflow unless you do a T somewhere, it will work, not factory correct but it was that way on my 4AD for over a decade with no issues, the correct way is too hook up to the rear carb as Phillip as said.

[Phillip]

Interesting points Mike.

This was a low-mileage and almost totally original 4AD-T that had been locked away since 1963. Those pipes were only removed and cleaned. The car had never been dismantled. I think from memory that the pipes may have been pinched at the ends, which makes sense, but we sold that car some years ago!

[mikeyr]

well we all know how Singer worked in those days...maybe "bob" whose job it was to put on skinny short pipes was sick that day and "joe" used what pipes he had on his bench, but I have never seen pipes that large when I could confirm they were original.

Either way, they have to be pinched to minimize the vacuum leak, those big pipes would be one heck of a vacuum leak if not pinched, the "pinch" is quite good, just enough to allow excess fuel to drip a little. Its actually more to break the siphon from the carbs so the engine does not siphon the gas from the carbs into the cylinders then it is to allow fuel to drip, but it will drip. By the way, its not required, if you want to plug those holes the car will run fine, but on really hot days or when parked on a hill, you may get excess fuel into the cylinders and come back to the car flooded and not able to start it without a hassle, you will find it actually runs better plugged but may flood.

On my car, I joined the 2 pipes thinking that would equalize the 2 carbs better, did it work ? no idea if it did, but parked on steep incline in San Francisco for a half hour and the car stank of fuel and would not start, luckily it was downhill until it started

[Peter McKercher]

The ones on my Nine Sports are that length, Mike. I've also spoken to several folks who recommend blocking them off entirely to improve idle.