small pin drill bits sets can be found in many industrial tool supply stores.
princess auto etc.
I do it by hand. Very small changes make a big difference +/-.001 .002" hone the hole by hand.
very easy to get carried away.
What happens if you just simply reduce-restrict the PCV valve air flow? this should richen the whole idle circuit by default. If it helps just get a different PCV valve that flows less at idle. (smaller internal orrifice)
A lot easier to "trim" the idle circuit by manipulating the PCV valve air flow at idle.
There is a possibilty your PCV is out of spec. Non OEM part. Something simple to look at , first.
Get a AFR gauge to see if it is in fact lean. @ offidle transition. I do all my tuning with a simple low cost 3wire Heated narrow band type.
if when the idle mix is set at idle , the idle mix screws are less than 2 turns out, I doubt the idle circuit IFR is too small.
It is very very rare that you need to start drilling this and that, especially when other things can be manipulated, like the PCV valve idle flow spec.
Last edited by F-BIRD'88; 04-24-2013 at 01:50 PM.