These guys replaced their blown golf cart motor with a cheap Harbor Freight 6.5hp and it works great. He took his Yamaha G1 that had a blown engine on it and replaced it with a Harbor Freight 6.5hp 212cc Predator motor. He also had to use a 3/4″ clutch adapter to up size the shaft to mount the larger sized golf cart pulley.
For a smaller than stock golf cart motor it sure gets the job done while going up and down the hills in his neighborhood.
This would make a great cheap golf cart build project to teach the kids a thing or two. If you could find a free or very cheap golf cart with a blown motor as your base it would be great. A new Predator 6.5hp motor can be had for around $130 and under $100 for the extra parts to install, convert and mount the new engine in the golf cart.
These Predator 6.5hp motors rate very high for such a cheap price and are easily upgraded with performance parts. While adding a 22 HP (670cc) V-Twin gas engine might give you some added speed and torque to your cart they are also much more expensive at $700 plus the conversion parts.
I personally have used those motors in a go-kart I built for my daughter and I later swapped it over to a mini bike I gave to my nephew. The only thing I ever had to do was change the oil, plug, and the air filter. The thing is still running after four years with no issues.
If anybody gives their cart a engine swap let me know how it went and I will post pics of your builds if you want me to.