Hyundai generator issue - any ideas?

[Monkeysmate]

If any of you mechanicy types have any ideas why my genny has started struggling I'd be grateful. When it's running, and I apply a load to it that it could handle very happily a couple of weeks back, the engine strains, the revs drop, and it trips. All the while it is running there is a background hissing noise, which wasn't there before, and when the genny stops, the hissing stops with one final "spit". Any suggestions would be gratefully received. Ta

[Wig]

Sounds to me like its losing compression through the head gasket or loose spark plug.

[Monkeysmate]

Great. Thanks. I'll start with that.
Ta

[RudeTony]

If the noise is constant I would be looking more towards a perished breather pipe or similar. Compression hissing wouldn't normally be constant but more quick on and off

[Monkeysmate]

Thanks guys, I've started pulling it apart and it seems to be a blocked exhaust filter/spark arrestor that was causing the engine to choke itself.