Accelerator pump check valve/ball
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
On Dellorto VHB 29 carburetores, there is a little ball inside the accelerator pump. The ball is solid and made out of some sort of plastic that is very resistant to nasty chemicals. I've even accidentally let them soak in carb cleaner only to find no damage. They seem to last forever, but if you need to check yours to see if it has worn, the size should be 3.175 mm or 0.125 inch or 1⁄8 inch.