Ever tried small tapered reamers? They are better than drill bits when opening up these holes as they leave no "rifleing" marks in the barrel of the jet, which can mess up the fuel flowing thru that reworked jet (so they say). I have a set of 5 reamers that go from say .100" down to perhaps .020" and have perhaps 2' to 2-1/2" of usuable length- mine have a pentagon shape (5 cutting edges-cant perfectly measure the actual dia. of reamer with micrometer as you could with a square, hexagon, or other geometric shape with diametrically opposed edges-but still quite,quite close) and can produce a mirror like finish on the interior barrel surface. Dont remember where I got them-most likely from McMaster-Carr, they are good for such things.
For tiny drill bits check out the model railroad folks like Walthers- they have sets so small that some drills look like "whiskers" in diameter.
Later,
Edski
