Your float valve question: it looks as if you've been "Keystered", like so many have. The aftermarket Keyster float valves frequently have springs in them that are stiffer than the OEM float valves were. Compare your old ones to the new ones to see how different they are.
This causes the float bowls levels to run a little lower, and also causes the dimples to really aggravate the stuck-open issue. So, I have been changing the float levels on the 350F/400F carbs with the Keyster valves to be 1.0 to 1.5mm "deeper" float bowls than stock. It helps, and cools down the engine a little with the richer mix. It makes about a 3%-5% difference in the mix, which is enough to make the engines run hotter.
The straight-weight 30w oils become approximately 10w when pushed beyond 200 degrees. They hold their weight pretty well until 190 degrees or so, then sharply drop in viscosity because they lack viscosity enhancers (i.e., long-chain polymer molecules). Technically speaking, once you get the engine heat under control again, 30w makes a pretty good summertime choice except for touring. It does make the engines pretty cold-blooded, though, as it is thick when cold.
The original CB750K0 sandcast owner's manuals recommended either 20w50 or 30w "high-grade", low-detergent, automotive oils (in 1960s parlance). This meant high-zinc, low detergent, mineral- or petro-based oils (not paraffin-based, like Pennzoil or Quaker State oils). The reason: the wet clutch hates paraffin-based oils (clogs the cork pores), and it does little for the plain bearing crank/rods when hot. Many of my friends in those days ran 30w Valvoline or Castrol in their 750s in the summer, 10w50 Castrol in winter, to save a few $$ over the Castrol XLR (which may be the best oil ever made for these SOHC4 engines! - now gone...).
