Sorry, no experience of Keihin PWK. But I have a Mikuni VM on the Velo. Works well. On the B40WD (which has about same space as a VS), I've fitted a sock foam filter. Have them also on the Honda 250 racer and the Vincent. On the racer, no noticable difference in air fuel ratio, with or without them. Don't know who makes them (maybe Ramair), got mine from Vincent spares company. Just slip it over the intake, no tool needed. One thing about Mikunis and Keihins that I don't like is all different needles available. Amal is much easier, just a few ones.