WLA-1 CARB

[blackchevy3de]

I HAVE A WLA-1 carb on my 500t blower , my question is can someone tell me what the (piston assy is, number 12318539130) and what it does, im thinking its some kind of power valve, its brass has a oring, and spring

 

[exotion]

Without looking it up sounds like a mixture screw

 

[Rivets]

That piston assembly is used to apply mechanical pressure to the diaphragm of the internal fuel pump.