The change from the original 790cc engine in the bike I bought new to the last version of the 790cc motor was the subject of my class. It was a very good engine. The bores looked very fresh after the final tear down except for some salt abrasion, the valve gear was in good shape, too, and it went very fast considering what it was.
The 865cc engine was built from the 790cc one with flat slide carbs and big cams among other changes. It wore out very fast and it this was most likely caused by a rich mixture at the smaller throttle openings and lower rpms I use on the street. Reversion was a big problem with that engine. Also, the engine is flooded to start it when cold with the flat slides. The standard carbs use an enrichening circuit.
Money is tight around here and need to get a lot of years out of the 994cc engine. It was modeled this morning in PipeMax like this: the 994cc engine with the compression lowered from 11.5 to 1 to 10.4 to 1 using a thicker head gasket and the original 790cc cams. According to PipeMax, the valve sizes, curtain areas, and lifts are adequate for the bigger displacement at 7,400 rpm.
The plan is to use the 790cc cams, the standard CV carbs, the thicker head gasket, and the racing valve springs without the spacer shims on the street. The race setup will use the flat slide carbs, the thinner head gasket, and the shimmed springs. It is a bit of work to make the change back and forth every year. At this stage in life I have more time than money so this is no big deal.