This sounds greasy,but it does work.
Ideally you would use a screw that has good threads.Clean the screw and the hole in which you are repairing with Brake Kleen or carb cleaner.
Apply JB weld on the screw and use a small nail to run some on the inside of the hole.
Insert the screw till it is fully seated,Let cure for 24 hours.
After it is cured,remove screw and repeat.But when inserting screw tighten till tight,but don't wail right on to it.
I have repaired a stripped out float bowl screw with this method with great succss!