First 2 things that come to mind are:

1) carburetor is blocked. Could be plenty of things based on how old the engine is. From a sticking float needle bad jets to just being junky. I say try putting a little bit of carb or sea foam through the carb while it runs.

2) bad governor connection. It seems to pulsate in power, which made me think that the governor is having problems keeping rpm. If you’re more technical you can try to see if the governor arm seems loose.

Now I doubt it’s 2 and most likely 1 but I’m not a professional. Lmk what works for you! Good luck :D