Briggs and Stratton 4.5hp not priming

Got what I paid for: next to nothing for a leaf vacuum with a Tecumseh engine. Cleaned out the carb and it worked pretty well... and then the engine spat the spark plug out. It made a pretty impressive POP! and threw it 6 or 8 feet. I figured the last owner had installed the wrong plug, and replaced it with another plug. That other plug was likely also the wrong one but it fit, or threaded in at least, and then last week the engine spat the plug out again. I researched and got a correct replacement plug, but now the threads are stripped and the plug won't thread in at all. Is there a fix for this? In my mind's eye I envision a large-ish tap and a spark plug to work with the new threads. Am I close?

I have a "gimme" Honda EX1000 generator which runs flawlessly. I noted the engine speed was a little higher than normal, but didn't think too much of it. I tested it by plugging a trouble light into it. After the welding type flash left my eyes, I tested the 120v receptacle. Across hot and neutral I was getting 265 volts. Hot to ground 130+ and Neutral to ground 130+. I spooled the speed back keeping my meter plugged into the receptacle until it dropped to 126v or so. Does the engine speed have that much to do with what I get across the receptacle contacts?? Is it possible the generator is faulty?