Mystery of the stalling/backfiring mustang(related pics inside of mystery part)

[Doomstein]

I posted earlier about a 1984 mustang GT that was randomly stalling out and occasionally backfiring through the carb. It has a Holley 4160 4 brl carb. We tested it for vaccum leaks and there doesn't appear to be any, and adjusting the timing has had no effect. A custom engine builder in Lakeland said that the secondary diaphragm spring in the carb may be worn, causing the barrels to open up prematurely/randomly, flooding the engine.

One thing I noticed today, that I didn't catch earlier is a mysterious orange piece of rubber, that almost looks like a part of a Holley umbrella check valve that goes near the accellerator pump, except it has a perfect little hole where the stem should be. I found it in my air cleaner. Anybody know what this thing is.

 

[4rdnut]

Do yourself a favor and buy an edelbrock carburetor. They are so much easier to tune with metering rods that are simply removed from the top of carb and the jets are easily accessible without having to spill gas all over the place. The edelbrocks perform better for everyday driving.

 

[FoMoCo17]

I've seen a rubber part like this on other carburetors. It goes in the accelerator pump passage as like a one-way check valve. It actually has a longer piece of rubber attached so that you can pull it through the passage during assembly. The longer piece then is usually hanging inside the float chamber so that it is locked into the housing from moving. I noticed in your photo that this appears to be missing thus resulting in it falling out of the accelerator pump housing to carburetor housing bore. These rubber parts are normally contained in the rebuild kit with instructions on where and how to assemble them.