Any idea what this Carter AFB Carb part does?

[DannyGarcon]

I pulled apart the Carter AFB on my ‘65 Nailhead 401 to give it a cleaning and to fix a sticking float, but I spent too much time staring at this part trying to figure out its purpose. 
I scrolled through some parts diagrams but didn’t see it on there. It looks like a tiny diving board and has a small set screw on the underside to possibly adjust the tension. My last rebuild kit came with a gasket for it so surely it’s required… It also appears to be in the required position for a double pumper (opposite the primary pumper). 

I’ll include some photos for reference. 
Thanks in advance for helping me with the little things that keep me up at night. 

[gungeey]

That's a bimetallic spring that acts as a valve to give extra air at hot idle

[NTX5467]

Hot Idle Compensator.

 

In some situations, in very hot weather, the idle mixture could become too rich, so the item opened to allow more air into the idle circuit to prevent such richness.

 

NTX5467

[DannyGarcon]

That makes sense. I’ve never had any issues with a hot idle thankfully (Texas, non A/C).

[carbking]

As mentioned, original purpose was a hot idle compensator.

 

But Pontiac found a more nefarious use:

 

Take a look at the picture.

 

The item on the left is the Buick hot idle compensator.

 

The item in the center is the Pontiac hot idle compensator, with RPM and performance limiting "wings".

 

The item on the right is the "dummy" performance limiter added to manual transmission Pontiac AFB's to assure that the more expensive tripower engine would outperform the less expensive 4-barrel engine. Hot idle compensators are normally used ONLY on carburetors on engines with automatic transmissions, except the dummy!

 

Most of the tripower engines are rated 200 RPM higher than the 4-barrel engines. There is just enough air deflection and resistance to restrict WOT RPM. Note that since these are on the secondary side, performance is not impaired until WOT.

 

The numbers are the original Carter part numbers for the items.

 

Jon

Edited March 5 by carbking (see edit history)