65 Riv Carter AFB - holes?

[moran75]

Hi all

 

Re. my ‘65 Carter AFB - 3921S.

 

Out of Curiosity can someone tell me the purpose of the holes circled in green/red in the attached pic?

 

greens are my main interest …maybe some kind of extension of the idle vents in the primary Venturi ?

 

Reds - due to their position above the fuel bowl vents I’m also assuming they are linked in purpose….

 

can’t find any ref in manual /web …but might be looking in wrong place 😀

 

Thanks in advance 

 

kev

Edited December 23, 2021 by moran75 (see edit history)

[lrlforfun]

OK Kev: The pipes, I think go to the fuel bowl and holes may be vents. I've taken apart, cleaned and re-assembled many. That really isn't a legit re-build. I wish I knew what to check for as to correct old problems as these carbs when operating  properly are excellent. GM put millions on their cars for a longtime.  Mitch.

[moran75]

Many thanks…BTW Mike’s Carbuertors have a great manual available for Carter AFBs…seems to cover everything …but unfortunately not the ‘green’ holes !😀

[XframeFX]

I'm trouble-shooting my 1963 AFB. I swapped the primary rods left-for-right, but will have to wait until Spring to test. It was -38 Deg. C this morning here in Edmonton and peaked to -31 midday. Grande Prairie Alberta had -44 Deg. C this morning! Hagerty has a good deal with Canadians. No way I'm bringing my Riv out in this icy mess. Black ice everywhere! My Riviera has a block heater too!

 

As for those vents, My engine compartment always smells of fuel. Normal? I've been driving FI vehicles for so long that I can't remember how a carburetor equipped car should be.

[carbking]

The red holes are atmospheric bowl vents, which complement the internal vents (brass tubes with angled ends) inside the air cleaner.

 

It should be noted that the atmospheric vents allow air to ENTER the bowl cavity while the engine is running, due to a pressure differential with the internal vents. The air velocity generated from atmospheric vent to internal vent allows internal pressure to exit the bowl cavity, thereby not artificially changing the fuel calibration.

 

The green holes accomodate the primary (high speed) air bleed/percolator vents (the small brass tubes seen through the green holes).

 

Jon.

Edited December 28, 2021 by carbking (see edit history)

[Bloo]

Why do those red holes exist? Wouldn't they negate any advantage of having the bowl vents inside the air cleaner?

[carbking]

Bloo - see the edit, we were typing at the same time.

 

EDIT: I maybe didn't explain the venting sufficiently.

 

When the engine is running:

 

There is negative pressure at the tips of the internal (Carter calls them air cleaner) vents. 

There is atmospheric pressure at the external (Carter calls them atmospheric) vents.

 

This differential in pressure allows any increased bowl pressure (from fuel percolation) to be discharged through the internal vents. This will include fuel saturated air above the liquid fuel. The atmospheric vent can then act as an air supply of fresh air to the bowl. It goes without saying that air MUST be able to enter/exit the bowl to allow fuel to enter/exit the bowl. 

 

Excessive bowl pressure would change the bleed-over point for fuel flow FROM the jets to the engine. Thus the vents help to maintain the proper calibration.

 

It should be noted that Carter produced 505 different type AFB carbs; the vents are NOT the same on all of the AFB models, but they do serve the same functions.

 

Jon.

Edited December 28, 2021 by carbking (see edit history)

[carbking]

And to answer the John B. comment on smell:

 

Virtually all engines with carburetors will reek to a certain degree of gasoline odor when the ambient is greater than the temperature at which the liquid fuel begins to atomize. Some of the smog emission engines have charcoal canisters to "eliminate" this, but I have yet to see one that actually did.

 

The odor is one of the few (opinion) advantages that efi has over modern carburetors. Smog emission, and adaptability to rapid altitude change are others.  

 

Jon.

[MikeJS]

10 hours ago, XframeFX said:

No way I'm bringing my Riv out in this icy mess.

Oh, com'n John, where's your sense of adventure. Buick has always touted their winter performance... "Disagreeable weather never bothers a Buick"

 

(Haven't found a Riv in the snow ad yet, but...

 

Seriously, hope you get you carb issues sorted, and remember, it's only 81 days til spring...