We're really not allowed to call or email, I don't know why your number showed up, generally it'd be all X's.
I found a parts breakdown of your engine and unfortunately it's of a design that's difficult to check out. Some 2-cycles allow easy access to the connecting rod and piston assembly for inspection and replacement, yours doesn't. Something you can check is the flywheel, hopefully one of the fins is smacking the shroud or something else is loose. I can't tell how the flywheel is secured from the manual. It shows a keyslot in the crankshaft but no key nor a key on the parts list. So maybe the flywheel is slipping a little. Check that it's tight and doesn't spin loosely on the crank.
What's likely happening though is that the piston pin has a scored needle bearing or the pin is loose in the piston. This creates a lot of friction and will overheat an engine and cause it to shut down. Take a long screwdriver, put the handle end to your ear and put the other end to different areas of the engine, like a stethoscope. The clacking noise should be easy to pinpoint this way. If it appears to be internal to the engine, you can further check this by removing the flywheel shroud and the spark plug and turning the flywheel back and forth until you hear the clacking noise. It could also be one of the bearing assemblies on the crankshaft, but it sounds like piston slap or a rod knocking to me.
The other thing to check is that it could be the shaft in the electrical generator itself. If the bushings or bearings it rides on are faulty then it could make a similar noise as could a loose magnet in the generator.
I'm sure you're right that the engine is overheating and shutting down. The last thing I want to hear from a customer bringing something into the shop is that it's making a "clacking" noise and shutting down. Compounding this is your particular position right now. You need this generator to work. Unfortunately, there's not going to be a quick fix if there's an internal problem in the engine or generator. So we'll have to hope you can find something loose. If the noise is internal to the engine, I'd increase the ratio of oil to gas, maybe to 40:1 instead of the manual's recommendation of 50: This can cause its own problems and may foul the plug and won't stop the rod or whatever from knocking, but it might keep the engine in one piece a little longer if it is an internal engine problem.
This is the link to the manual. It should be of some help in looking for the problem. Thanks and let me know if you pinpoint the noise.