drilling out carb jets

[saaz]

Easier way is to drill until you get the size right, then invest in the right jets. Saves having to try a few sets of jets before you get the combination right. mIne are drilled out, have been dyno tuned and are ok after 18 years or so.

[Anonymous]

drilling jets

Drilling jets ??? Are you guys loonie ? At $2.50 a piece why bother . One day you may want the old size again. Besides these are precision made pieces that you could not hope to duplicate consistently unless you had a very good quality lathe to work with, not a hand drill or drill press. Any motorcycle shop will be able to supply them or find you mikuni distributor in the yellow pages or www.sudco.com online or ride with four totally different jet sizes . And you guys thought tuning was hard with the right parts

[Anonymous]

You sound like an engineer, Nashville Bill.

I also like to experiment, and would rather pay 25 bucks to find something out for myself, than to pay 12 bucks to have someone do it for me! 8)

A fixture in the drill press is a great idea, but a lathe is a better one, if it is available. That way, the hole will be centered all of the time.

As far as measuring the existing orifice goes, machinists use pin gages (the look like drills but are smooth) They come in sets, and are generally sized in .001" incriments. They are usually .0001 smaller than the size marked, so you can actually fit it into the hole you are measuring.

Regarding drill sizes, they generally come in three size designations, numbered (or letter for big ones), fractional (ie 1/8"), and metric. If you really want to dial in the flow, don't limit yourself to just numbered drills. Looking at my chart of standard drill sizes, it reads as follows:

#80 (.0135")
.35mm (.0138")
#79 (.0145")
1/64 (.0156")
.4mm (.0157")
and so on

Smaller drills are available too. They might come under the heading of Jewlers Drills or Watchmakers Drills. I'm not familiar with standard sizes below #80.

If you really want to get fancy, you can order a reamer ground to within .0001" of any diameter you want. Of course this isn't going to be cheap, but it is possible.

You could also pick up a countersink and add a chamfer, like the Mikuni factory jets. But without a lathe, it would probably be hard to get the chamfers on all four jets close to the same size.

A store that sells machine shop equipment and supplies can set you up with whatever you need. McMaster Carr is usually a more convenient source, and they have a web site.