[Weldangrind]

Buy an index of numbered bits from 61-80. Know right now that the bits will not necessarily be in the correct compartment of the index, so you need to measure the bit with at least a vernier caliper before drilling.


When you select an index, buy one that comes with a pin vise. A pin vise is a device about the size of a Sharpie with a collet in one end, to hold the bit. If you don't have a suitable way to hold the slow jet for drilling, you can just hold the jet in your fingers. Slowly and gently spin the jet onto the bit that you're holding stationary in the pin vise. With patience, the bit will find its way into the jet squarely and ease the hole open.


Back to measuring: insert various bits into the stock slow jet until you get a sense of which one is a close fit. Measure that bit and then search for one that is one size larger. Continue in that fashion, one step at a time, until the desired size is attained. The reason I prefer Mikuni is that jet sizing is tied to millimetres; a 25 slow jet is 0.25mm, so it's easy to make incremental steps without much fuss. A similar process with a Keihin jet requires a cross-reference chart to convert Mikuni (or millimetres) to Keihin.


I've followed this process several times with good success. When purchasing a cheap 61-80 index, it pays to buy two at once. That way, you're more likely to actually have a complete index with several spares.