Sealed 'R2' Avanti Carb!

[mfg]

I'm in the midst of a interesting debate with an Avanti owner who contends that what makes a sealed R2 Avanti Carter AFB carburetor 'uniquel' is its lower body half... (fuel bowls, venturis, etc)

I've always felt the sealed upper half (or air horn) is what actually makes a sealed R2 carb function as a sealed unit....the lower body being somewhat 'generic' with other period AFB's.

Thoughts?.....Anyone want to 'jump in' on this friendly difference of opinion?

Edited January 5, 2021 by mfg

[64studeavanti]

The body is quite a bit different from "generic" AFBs. The base of the R2 carb has slots to keep fuel from leaking around the shafts under boost. The body also contains the special non-collapsible floats and seals on the idle screws. Other than the tag, any air horn could be used. 

[mfg]

5 hours ago, 64studeavanti said:

The body is quite a bit different from "generic" AFBs. The base of the R2 carb has slots to keep fuel from leaking around the shafts under boost. The body also contains the special non-collapsible floats and seals on the idle screws. Other than the tag, any air horn could be used. 

Could a generic, unsealed, Carter AFB top cover, with factory vent holes and an unsealed accelerator pump opening, be used unmodified under supercharger boost?

Wouldn't gasoline spray all over the engine compartment?

[64studeavanti]

The seal for the accelerator pump is not part of the airhorn. The four vents are just plugged on the sealed airhorn. Any AFB airhorn could be similarly plugged. It would take quite a bit of machining to convert a regular AFB base to match the function of the sealed one. I believe that Bob Johnstone's site has instructions for the conversion.

[mfg]

29 minutes ago, 64studeavanti said:

The seal for the accelerator pump is not part of the airhorn. The four vents are just plugged on the sealed airhorn. Any AFB airhorn could be similarly plugged. It would take quite a bit of machining to convert a regular AFB base to match the function of the sealed one. I believe that Bob Johnstone's site has instructions for the conversion.

Correct, and that's the point!....unless modified in the way you describe, including machining for the accelerator pump seal, using a generic air horn would lead to possible disaster.....My friend did not seem to understand that! .....Ed

 

 

[64studeavanti]

I do not recall any special machining for the sealed accelerator pump. However, I will check in the morning. The 4 external vents just have small plugs driven into them. The base is what requires the machining not the airhorn!

[mfg]

2 hours ago, 64studeavanti said:

I do not recall any special machining for the sealed accelerator pump. However, I will check in the morning. The 4 external vents just have small plugs driven into them. The base is what requires the machining not the airhorn!

You are no doubt looking at a carburetor which someone has modified to work with a supercharger....not that uncommon over the years!

First off, a FACTORY sealed Avanti carb air horn would not have "plugs" driven into the air horn vent holes....they were never drilled out in the first place!!

Second, the accelerator pump seal is staked to a recess machined into the air horn....otherwise how would it ever stay in place??

Third, the "special non-collapsible floats" are not located in the lower housing (as you mention) but are pinned, L&R, to the air horn.

Also, explain what "machining" you feel the base (lower body) needs...and tell us the serial (model ) number of your AFB.......the number should be stamped into the left front mounting 'ear'. (as you face carb)

[64studeavanti]

The floats are removable - not part of the airhorn. The external vents are indeed plugged on my model 3507S airhorn with the "sealed" carb tag. Yes, the accelerator pump seal is staked in a recess - non-sealed AFBs have the same recess. The seal could be staked on non-sealed airhorns as well. 

If you bother to look at the base (the part that mounts to manifold) you would observe a substantial difference in the machining to control leakage via the throttle shafts under boost. 

 

In short, a non-sealed airhorn can easily become sealed by plugging the external vent holes and installing the pump seal in the existing recess as was done at the factory. The floats, not a permanent part of the airhorn would need to be used as well. If you are looking for authenticity,  you would also need to install the "sealed carb" label.

 

A non-sealed carb base requires significant machining to resemble a sealed one. Adding the seals for the idle screws is also trivial. 

 

Of course, you would need to use sealer on the screws as per the shop manual.

[mfg]

Sounds odd the air horn vent holes are plugged  on the 3507S you're dealing with...I presently have three of the sealed 'supercharger' Avanti carbs, and none of them have drilled vent holes..the 'boss' is present, but no drilling was done by Carter!!

[64studeavanti]

Maybe we are discussing different things. Standard AFBs have 4 external vents, one at each corner. This carb has them plugged. Where is the vent you indicate located?

[mfg]

2 hours ago, 64studeavanti said:

Maybe we are discussing different things. Standard AFBs have 4 external vents, one at each corner. This carb has them plugged. Where is the vent you indicate located?

Yes, I'm with you on the location of the four vents in the air horn......On my sealed carbs, the bosses for the vent holes are there, but they were never 'opened'  (or drilled out) by the factory.

Other R2 type carbs I've dealt with have been this same way....that's why i thought it was unusual that the air horn of your carb indeed has the four vent holes drilled through, (like you'd find with an R1 carb),....and then the holes were plugged with...??? (solid metal pin?...epoxy?)

INTERESTING!!!!!

[64studeavanti]

They look like pins. I will post a picture if I can figure out how.

[John C]

3721sa afb 63 Corvette ,Plug 1 vent in the rear of the air horn and bolt it on. There are not 4 vent holes in the top. Take a look.  John C.

[mfg]

10 hours ago, John C said:

3721sa afb 63 Corvette ,Plug 1 vent in the rear of the air horn and bolt it on. There are not 4 vent holes in the top. Take a look.  John C.

OK, that sounds like it would work.

The 'old dog'(me) learned something!.......

Last night I rummaged through a pile of non-Stude Carter AFB's....now I thought all non-sealed AFB's had the four air horn vent holes...but that's not so!

John C found one (Corvette) without the vents,...and I found an early AFB, which came off a 1957 Chrysler, that also doesn't have the bosses for the four vents drilled through.......This Chrysler air horn could be used to build up an Avanti 'sealed carb' clone....The only thing about the Chrysler top which would not be correct from an originality standpoint is the fuel inlet is on the side of airhorn...not the front.

[John C]

Maybe we all learned a little something, self included! 

[mfg]

1 hour ago, John C said:

Maybe we all learned a little something, self included! 

Yes!...I also now 'get' what '64studeavanti' meant by machine work on the lower body of carb....I thought he meant somewhere inside the bowl area....He's (I believe) speaking of the grooves cut into the base, which dumps supercharger pressure into the manifold if it should enter the throttle shaft (both) bores.

[mfg]

As an aside......I was never very impressed with the idea of pushing blower pressure through a carburetor which has been sealed....frankly, hoping that the seals hold!!

Studebaker got it right when they put that aluminum housing (R3) around the carb, eliminating the need to seal it.

Studebaker had successfully used an aluminum housing around the carburetor of the '57-'58 supercharged Golden Hawks, and it beats me why the engineers didn't enclose the carburetor of Avanti R2 models in a housing from the get go!

[studegary]

13 hours ago, mfg said:

As an aside......I was never very impressed with the idea of pushing blower pressure through a carburetor which has been sealed....frankly, hoping that the seals hold!!

Studebaker got it right when they put that aluminum housing (R3) around the carb, eliminating the need to seal it.

Studebaker had successfully used an aluminum housing around the carburetor of the '57-'58 supercharged Golden Hawks, and it beats me why the engineers didn't enclose the carburetor of Avanti R2 models in a housing from the get go!

Cost

[brad]

If one wanted to convert to a newer Edelbrock carb, the marine version is sealed and will work out of the box. If you want to convert an R1 AFB to an R2. I have done it with no consequences. I solder a brass nail through the floats to stiffen them up. Plug the top fuel bowl vents. Counter bore the idle mixture screw holes slightly for an "O-ring".  Use the afore mentioned Edelbrock MARINE accelerator pump seal(throw the actual plunger away it doesn't fit) and use the factory plunger. 

[mfg]

13 hours ago, brad said:

If one wanted to convert to a newer Edelbrock carb, the marine version is sealed and will work out of the box. If you want to convert an R1 AFB to an R2. I have done it with no consequences. I solder a brass nail through the floats to stiffen them up. Plug the top fuel bowl vents. Counter bore the idle mixture screw holes slightly for an "O-ring".  Use the afore mentioned Edelbrock MARINE accelerator pump seal(throw the actual plunger away it doesn't fit) and use the factory plunger. 

Thanks for this info brad!