If you put a tap into it you've enlarged the bottom part of the emulsifier, below the lateral holes Mark. I think it would probably give different mixture results after doing that. I also don't think it is very likely that having an internal thread in the emulsifier will help you to screw it out, unless you use a left hand thread with a shoulder in just the right place, so you screw it in until the shoulder bottoms, then keep turning. Likely to work I think, but left hand taps and matching dies (to make the shouldered screw) of obscure sizes might be difficult to come by.
If you are determined to do something, I can make a suggestion of the "end up with something that is better than nothing" type. Can't say I recommend it, because it is crude at best.
If you get hold of a splined-type stud extractor that fits into the bottom of the emulsifier (but cuts spline recesses when it does so), provided you have soaked the carburetor enough to soften the gum thoroughly, you should be able to unscrew the emulsifier by unscrewing the the stud extractor. Then solder the hole where the internal splines have been cut, and re-drill it to the orignial size. (Soldering and re-drilling brass jets is a traditional practice for old-timers like me.) Re-drill any lateral holes that have become soldered up. The only cost involved is for the splined stud extractor, and that should be a permanent tool you have from then on.
