981cc for the 920
We now have 95mm 981cc 8.8:1 piston sets for XV920s. Stock, Yamaha claimed 8.3:1. From shear displacement increase there will be more power across the board -- especially down low. To really benefit, while the engine is out and torn down, it would be an excellent opportunity to add sports cams and springs, a free-flowing exhaust, and maybe some carbs. These will fit all 920s: Virago, Midnight, and Chain-drive. Note that you can't simply run thousand cylinders -- the sleeves have a larger OD; they won't fit the 920 cases without some machine work; either to enlarge the spigot hole in the cases, or to turn down the thousand's sleeves a mm or two to fit the 920 cases. Back when I first got my Euro (chain-drive) I ran 96mm pistons and rings (with a surfaced head) for 100k miles until the front head gasket blew, then another 125k miles before the rings started blowing-by enough to make me pull the top-end again. [BTW -- the same rear gasket has been on the engine for 370k miles so far; same pins and clips, and rubber gaskets too] The 95mm "kit" is actually just some cleaned up XV1000 Virago pistons with a set of new after-market rings. They shall be bored into a pair of 920 cylinders, which have been blasted and freshly painted. The greater swept volume into the 920 combustion chamber yields approximately an eight point eight compression ratio. I just blasted the barrels and shot them black. If that does not suit you, the paint will strip or blast off, but keep in mind these are thirty years old; I'd suggest just leaving them.
You will feel a difference. Just leaving everything else as it is will yield gains across the board.
A re-cap: these cylinders have been bored and are sporting a nice 45 degree cross-hatch. I spent some time polishing the gasket surfaces with a buffing wheel -- you can hardly tell. The pins are a slip fit in the pistons, the dowel holes have been dressed to allow easy assembly. Everything has been doused in a light machine oil to preclude corrosion and then wrapped in plastic. I recommend a thorough scrubbing with dish detergent and water just before assembly. Slip it together dry except for a dab of assembly lube on the piston skirts and pins. The dry rings will quickly mate with the cylinder walls and all will be lubricated within a minute of start up.
As soon as we get some units to model from, there should be a 805cc 11:1 kit for the 750. The problem we are having is that the 750s we get are late models, and the requests we get are for early models. All the part numbers are different and the cylinder deck is recessed on the early; flat on the late. So frankly, I'm not sure what to do. I think that the late models were poor sellers.
Eleven hundred pistons should be available within a couple of months. As for 700s: just run late model 750 pistons and rings. It'll boost your power slightly. Face it: you're never going to make one of them scary fast.