So, Fiche Index says "E17-1"... Fiche "E17-1" marks the part as number "16"... Part Number "16" = 16111MV4000
Off to DavidSilverSpares...
16111MV4000 = PISTON,VACUUM !D >>> DISCONTINUED
Help! - Anyone know a source for these?

FYI...
Part number 16010MV4000 has been superceded by Part number 16010MV4780... which is GASKET SET,A *G (What appears to be all the gaskets and o-rings) is available although this part will be special ordered in for you from Honda. Delivery time should be between 5 - 7 working days depending on stock availability from Honda. For the sum of £14.63 (inc VAT) per Carb.