Even with JIS bits, 2 of the 4 throttle plate screw cross-point heads stripped when attemting to remove the throttle plates from the spare carbs. Major bummer. Alden Micro-Grabit #1647P bolt extractor to the rescue...
Using the Micro-Grabit is an art in itself. I now know how.
The throttle plate screws are M4x5mm narrow-head, flat-topped, shallow taper, & countersunk, so there's not much to work with. They are also peened from the other side. Glad they extracted without any shaft or plate damage.
The replacement screws are super-rare. I am awaiting some RC car screws that should work. In the interim, I drilled new air bleed holes, at 90 degrees, in the replacement plates in the same basic location as before. Again, I used a pin-vice and drilled by hand. First pass was .98mm and the second pass was 1.2mm.
I'm gonna try 1.2mm to start, with OEM Keihin 42 pilot jets.
From what I know at this point, optimum air bleed diameter is most likely in the 1.2mm - 1.4mm range, depending upon tuning objectives & setup.
I really don't want to wait for the replacement screws & might roll the dice with the on-board carbs in removing the existing 1.6mm throttle plates & replacing with the 1.2's.
At the very least the reused OEM throttle plate screws will get blue loctite, maybe red; I have not decided. The screws will also be shortened slightly so they are flush with the mounts.
I will also smooth the leading edges of the throttle plate shaft "sandwich" mounts.
I think the 1.2mm air bleed holes will be OK with the 42 pilot jets. We'll see. The art is in balancing the air bleed diameter, pilot jet size, and pilot screw settings to get a decent idle and a perfect cruise...
