The OIL Question: If you ask this question of a thousand owners, you will get a thousand different answers.
As long as you use a good quality oil that does not have any additives which will cause the clutch to slip, you are fine. Many people are using 15w50 Rotella or Mobil 1 15w50 in warm weather. These oils are high mileage oils and Rotella is made for diesel engines. Others use Amsoil. I use a good quality regular automotive oil such as Castrol GTX 20w50 or Valvoline 20w50 in warm weather, then drop down to a 10w40 for cooler weather following the manufacturers specs. I don't feel paying $10 per quart for motorcycle specific oils such as Yamalube is worth the cost. If you look at the specs for the oils you will find most of the quality dino oils are close to the same.
I would suggest using Mobil 1 Racing 4T Fully synthetic 10w-40. You can buy it directly from Mobil for about $70.00 actually pretty cheap considering the motorcycle oils are pretty expensive. I have been satisfied and I have used synthetic motor oil in my cars and they really keep the engine in excellent condition. It doesnt break down with heat like the petroleum based motor oils. The oil in the Viragos get very hot and its better to use the synthetic type. It is safe for the wet clutch and the transmission also. They will not sell anything less than a case of six, but it is still cheaper than $15.00 a quart for motorcycle oil from the dealership of otherwise. J&P Cycles has genuine Yamaha 10w40 for 6.99 a quart and that is not synthetic. mmmm I am sold on the Mobile 1
Jimmie Geraghty 1983 Virago 920 Midnight 7000 original miles