Motorcycle Repair: 1982 CX500C Master Cylinder Bypass Port, calcium buildup, carburetor bodies

Question
1982 CX500C Master Cylinder Bypass Port - I have the master cylinder off and disassembled, the bypass orifice is plugged solid with dried crud (maybe corrosion?).  I have soaked it with Berryman B-12 (carb cleaner) to no avail.  Do you know the approximate diameter of the passage? I have read random descriptions of anything from .010 to .015 inches.  I don't want to poke at it with anything larger than the passage, for fear of ruining the casting by making
the hole too large. I have found a source of micro drill bits, as small as .006 mm (less than three-thousandths of an inch), I may have to go that route, I'm afraid the orifice is plugged with "white rust", there was some elsewhere on the innards.  Thanks for your help.

Answer
Craig, I don't have anything around here to check, but I think that going in with something like .010" is safe enough.

If you have a small scribe with a 90 degree tip, you might be able to try from the inside the bore and poke the passage from the bottom.

Some CLR might be helpful for any calcium buildup... Some people use white vinegar, brought to a boil to clean old carburetor bodies.

Bill Silver