Honda GX390
The GX390 is a 389cc OHV engine with 11.7 hp at 3600 rpm, and 19.5 lb ft of torque at 2500 rpm. It's a counter clockwise rotation, if looking at the PTO side. They come with a 1" crankshaft that will adapt to many primary clutches for golf carts. Since 2010 they have been equipped with a digital CDI ignition system. Max rpm on these engines in stock form is 3600 rpm, which is good enough for around 18-20 mph on most stock golf carts, very similar to stock speeds.
The idle speed is set at 1400 rpm from the factory, so shifting from neutral to forward or reverse might be a sticking point, with some grinding and hard engagement. To combat this, several manufacturers have introduced an "adjustable" carb replacement. While not perfectly ideal, the idle can be set to around 1100-1200 rpm, which will work with most golf carts. Some adjusting to the idle is likely needed with this engine.
Honda has been manufacturing small engines since the 1950's. The GX series engines have been in production and use since 1983. Millions of these engines have been used to repower generators, pressurewashers, lawn mowers, small equipment, and more. Decades of reliability are proven.
Many manufacturers have copied this design, which we call "Clones". Two popular and respected clones of the GX390 would be the Predator 420 and the Duromax 440. Both have shown to be viable engine replacements for small equipment. Some parts are interchangeable from one engine to another, but not all. You can find many members of BGW who have used different versions of this engine with good success. Some have even modified their engines for high performance use.
Attached is a copy of the Honda GX390 manual.
You can find more info on the Honda GX390 at
https://en.honda-powerproducts.com/
Duromax engines website
https://www.duromaxpower.com/collections/engines
Predator engines website
https://www.harborfreight.com/engine...s-engines.html