After 4+ decades of Castrol 20w-50 I am switching (per Hondaman) to the Valvoline 4-stroke motorcycle oil 20w-50 DINO. I also add zinc. Dan
I had pretty good luck with the Valvoline stuff, with added zinc to smooth out the clutch on takeoff, and not be so sticky. Then I found some of the Bel-Ray (it's hard to find here) and put in their EXL Mineral type in 20w50. It immediately (within a couple miles) ran quieter, idled better, and shifted smoother. As I kept using it (until the cold stopped me) this Fall, the bike got smoother and smoother. Since it was just rebuilt, some of this is the break-in, but the noise issue is not: the suddenly-quiet engine, silky clutch, and easy-to-find Neutral tells a [good] story about the EXL. Expensive, though!
...and, it is a mineral oil, which has long been my favorite type. That's been gone in these parts for decades. The mineral oils are naturally non-sudsy, so even if the manufacturer added detergents, they will wear out quickly (by design) and leave the bike with non-foaming oil.
The most immediate difference I found between the Valvoline and the EXL: after a 90 MPH run with the Valvoline and hitting an offramp to wait for a traffic light (i.e., typical north Denver riding style), the Valvoline would display some foam in the oil tank. The EXL shows none. This performance is much like the old Castrol XLR mineral oils that were so excellent for these engines, but vanished in 1996. I can't give further evaluation until this sub-zero winter leaves, grr...