SAE 20W-50 according to the Haynes manual
The oil capacity for the Yamaha Big Bear 400 is 3.2 quarts. It is recommended you use 10w30 oil in the Big Bear.
You can use 10W30 or 20w50.
SAE 10w30 Full Synthetic, any major brand.
I believe Yamaha came out with oil injection. You do not mix the oil with the gasoline - the oil is in its own reservoir and mixes automatically.
The Yamaha 400 Kodiak all terrain vehicle takes 2.6 liters of oil to fill to capacity the oil tank. That amount is approximately 2 and one thirds quarts of oil.
10w-40 is recommended
yamalube 10w30
20w/50
As much as it wants.
20w50
2 Litres
3.2 quarts