Maybe I`m blind, but I`ve had my PHBL 25mm to bits quite a few times changing jets & I`ve never seen an anti surge washer in the float bowl - I assume looking at the parts diagram it just sits over the jet to stop fuel slopping about when you`re going for it?
For what it`s worth, mine has been on a 190 cylinder & I never noticed any bad running on acceleration/cornering.