Oldtruck1946,
My preference would be a Heli-Coil thread repair, but I would bet there isn't enough material in that casting to accommodate it. The next best thing would be to figure out what thread configuration you have now and step up to a metric screw.
If I recall, those screws are a 10/32 thread. A 12/24 would be too large so I would see about a M5X.8 metric screw.
This all might seem confusing, but if you take the screw to a good hardware store, one with lots of screw bins, I'll bet you could find something just a tad bigger that would clamp and hold.
You would probably have to get the corresponding metric tap, or if the metric screw was just a smidgen larger, it might self tap into the soft pot metal material of the carburetor bowl.
If you look at the page I linked, you will see that M5X.8 is just a couple of thousandths larger than a #10 screw.
Ask one of the 'helpful hardware men' to give you a hand!
http://www.precisionscrewandbolt.com/metric.htmStuart
