Simple Mikuni main jet holder

An annoying thing is how to organise your jets. A while back I discovered that the Mikuni thread for the large hex main jets (‘hexmain’) is an odd thread size but roughly works out to be British Association #1 (~M5.3 x 0.9). These taps are available in a range of places, e.g. ebay, and you just need a 4.5 mm drill bit as the appropriate tap drill.

It’s pretty nice to make up a nice 3-4 mm aluminium plate and chuck in appropriate holes. Much nicer in the toolbox and much quicker to sort through your jets at the track.


That happens to be a main jet setup for a VJ21 RGV250 running standard VM34ss (1990 model VJ21). The engraving is crud but you don’t always get paid for good looks.