I'm sure there are better high-tech ways of doing this. I did it literally free.
Only time used was;
- taking a knife and shaving off the nipple on the bottom of the bowl to make a flat surface.
- finding a proper sized drill bit to remove the shaft of the screw but leave all the threads.
- drilling the hole.
- grind off the end of the screw that protrudes into the bowl.
I had the carb off already replacing the needle valve and seat. The screw method seams to seal well, doesn't leak.
I went to the plumbing store looking for a 90 degree brass valve or another means when my son says, "your going to drill a hole in your carburetor, install a brass valve that is held with what, silicone?" then it hit me, drill a hole & put a self-tapping screw in the hole! The parts were adding up to over $10.00, the screw hole is small and if it didn't work or a better method arises I could always drill a bigger hole and put a valve in later.