With a series of Mikuni carburetors, but also on gleihins from Honda’s Bol d’or or CX 500, the holes for the idle nozzle are closed with a rubber stopper. The idle nozzle is thus supplied with fuel by a lateral bore through the main nozzle. The things mutate with the years in the fuel into chewing gum and are a recurring annoyance, currently on the Mikuni – carburetor of an 82er 650 Katana.. Can anyone explain to me meaning and purpose of this construction?