Any major brand 100% synthetic in the correct weight which is more than likely SAE 10w30.
you can use standard ATV oil from places like tractor supply. or you could use a 30 weight oil
ATV 10-30 for most weather
for my three wheeler i just use regular 10-w40 engine oil it works great is cheap and easy to get
motorcycle 10W40
10w-30 is a general all around good oil and about 1.3-1.5 quarts
A 10w40 oil with an American Petroleum Institute or API rating of SF or SG.
Will 10w30 oil be ok for a hondatrx90four wheeler
NO
1 quart
The oil capacity on a "2002 Honda Foreman" is, 3 quarts.
Honda would maintain that is correct but others would say you can use any JASO MA approved oil.
You need an air filter and a fuel filter. On the larger models there is also an oil filter.