Hey all. Apparently trying to drill a .070" hole down an M5 screw isn't all that easy even with a lathe. I haven't given up on that but I tried another approach today and it seems to have worked.
I tapped the hole with M5 X 0.8 where the 2-stroke oil used to go into the carb. Then I got some 3/16th copper tubing. A foot of it cost $2. Sanded down an inch or so of it, enough to engage an M5 X 0.8 die. Threaded the copper tubing and screwed it into the carb. It seems pretty sturdy. It think this will work. I haven't trimmed it to the length or position I want yet but it's screwed in tightly. (edited)