Swap engines on Portable Generator?

Okay, so I have a portable generator that has mounted on it a Briggs and Stratton engine I believe 3.5 horse power or something. The engine has mounted on it a vacuum carburetor and in this carburetor a little piece of rubber (thin rubber) has torn. I cannot find more of this material nor do I have the know how to replace it so the engine is basically kaput. So my idea was to mount another engine on it. Maybe a Predator 212 or something like that. Is it possible? and If I were to put a bigger engine on it, would I get more watts out of it? Thanks!