LemuelMiranda
You can definitely install a larger engine, but you’ll need to make sure it fits the space and aligns with the tapered shaft setup. Since Tecumseh is out of business, you might need to modify the mounting or find an adapter for the shaft. Just make sure the new engine's power output matches your generator's needs to avoid any issues.

Issue I’m finding is engines like Predator are keyed shaft not tapered shaft.

I learned years ago you can’t take a battery inverter and battery charger and have endless energy.
And I don’t want to do this but can you use a smaller generator like a 3500watt to power an electrical motor that would drive my 5000 watt genhead powered by an electrical motor ???

Tecumseh seemed to have an issue with governor shaft oil leaks. I didn’t bother checking oil bc it’s suppose to have low oil shut off and I was only warming engine to change the oil. And slung a rod

Is there an adapter to convert the harbor freight type engines to tapered??
Most people do the opposite of me and want to repurpose engine for a go cart.

Not that I've heard of....  Doesn't mean it doesn't exist..