http://www.pqiamerica.com/
Find a brand that passes PQIA testing, and is in the proper weight according to the owners manual... and try to go with a "Global" Owners Manual... not one that is "only for the US, energy conserving EPA Market"...
Usually a "wet clutch" system can handle conventional or synthetic oil in: 10w-30, 10w-40, 15w-40, 5w-40 (synthetic), and in some cases they like something as thick as a 20w-50 synthetic oil
Most wet clutch systems don't get along with the "Energy Conserving Star" 5w-30 oils... I haven't tested a 5w-30 in our Lifan engine, as it seemed happy on the cheapo Rotella or Super Tech 15w-40 the one time I used them (didn't have my usual 5w-40 on hand) and the rest of the oil changes have been with 5w-40 Rotella
It's only $12 or so for a gallon of Super Tech 15w-40, and $18 or so for Rotella synthetic 5w-40...
Best to go out, buy a brand and weight of oil to test out in your machine... from what I can see... they all have their own "likes, dislikes, and personalities" (just like their owners
)