Jerry,
You can go with the Gx50 if you must but they're really not
engineered for a bike. You'd have to disable the oil sensor &
governor. If for any reason you'd have to lay it down you'd get
a carb full of oil. I'm not knocking the engine;it's well made
and reliable, but for a bike going up from an EHO 35 or a GX35,
The Tanaka PF4000 40cc makes more power, is lighter, and
can run at much higher rpm. EPA and CARB approved, it's
a little louder, but just as reliable with a great warranty.
Yeah, it's a 2 stroke, but out out performs the honda GX50.
I've done both. If you're lookin to upgrade the Tanaka will not
disappoint you.
P.S. I still love my little GX35 on my other bike.