ol doc gully

hole was smaller than the 1.25mm bit so i ordered 2x 1mm bits off of mcmaster (smallest they had). seemed to have fit perfectly, a little snug, i cant tell that it fit any tighter at the top versus the bottom (indicating that it was indeed a tapered orifice). luckily the screw had broken off slightly below the surface so it left a solid holster for the bit. drilled it out with little drama, seems to have gone well. the exit shape as viewed from the throat is less than perfect, though the needle fitment appears to be well aligned. and im not sure how to check or what to do to make sure the needle valve screw mating surface is back in original shape so im just leaving it. just hope i can get this one to idle like the others...

update... havent got to check with the guru yet, but asking the chemists and metallurgists around sounds like the reaction of nitric acid with aluminum is the biggest question mark. it may be more likely for low concentrations to react unfavorably with the aluminum, while higher will just leave a small amount of oxidization on the surface. im not sure but it seems like enough uncertainty that id rather not go that route. i acquired several drill bits ranging from 1.25-1.45 mm so i should be able to figure out the diameter this evening, assuming it is within that range. not sure if the screw edge is recessed enough that the drill bit wont walk on me, but might have to do something to prevent that. i looked at it under different lights and angles and best i can tell it is not tapered.

yeah, i cant get a good picture, but it looks like the initial seat just below the threads has a quick/shallow taper but then the orifice going down into the throat looks straight walled...? thanks very much for your help and input

Ah, nitric acid, very good to know, that should be enough to get me started in really figuring this out - thank you. The main reason I've been debating it is because I fear that the passage below the seat (45 DCOE 152) is tapered, so that if i were to drill it, it would not be right - can anybody confirm or deny this? I already have a 1/16" bit that looks to be just about the right size... tried heating and forcing back through from the carb throat but it only bent broke and mushroomed

any chance youve found any more info on that acid? i have the exact same problem, although thankfully only one needle broke. was just about to drill it out and came across this, i have some chemist friends that can hopefully help shed some light...