At the bottom of the accelerator pump well there is a check ball and a retainer clip. If you lose the clip don't panic. I suspect the check ball will stay in place without it.

Polish the pump well with crocus cloth so that it is very smooth. Today's fuel has little lubrication which is bad for the pump cup. It needs a smooth surface to glide smoothly.

There are many different types of Aisan accelerator pumps, you can find them all here with images and dimensions. Don’t forget the pump boot!