Hello N,
These calibrated pilot air bleed jets have to work in concert with the main fuel jetting tolerances. Changing main jets is an option but usually but results in an over lean or over rich condition. This is where the bleed air jetting is vital to get the desired air/fuel mixture atomization.
It also helps to have more than one set of pin drill bits handy along with extra donor pilot jets in case things go south. I've robbed a few out of Honda clone and similar aftermarket carburetors.
I also like to use the phrase: "Sometimes you have to slow down to speed up". So, it requires a lot of patience.
A drop of light machine oil or WD-40 on the bit helps along with a very sensitive touch. When I feel the bit grab even the slightest, I pull back and brush off the micro brass particles on the tip of the bit. This is what I refer to as "Knipping" at the tiny brass insert material. This also prevents side load catching of the bit which will quickly snap the bit. The brass inserts are not very thick at all and is only a small, calibrated portion of the plastic jet holder.
I'm fairly certain when these are initially drilled to tolerance a very high-speed drill (similar to a dentist drill) on a fixture is used and the plastic pilot jet bodies are inserted into an anvil fixture for stability. The tolerances for the jet calibration machines must be in the incredibly strict.
When we are attempting to drill them by hand, it is a "shot in the dark" if it will resolve a surging problem or just make the condition worse/better. Fortunately, I've had decent luck the few times I have done it.
Life was much simpler when carburetors had air and fuel mixture adjustment screws. Thanks to stricter emissions regulations and "cookie cutter" automated mass production, those days are long gone.
