Continuing...
Installed the new cap and went for a ride today. Bike now revs a bit more before acting the same way: more throttle results in a bog, with sputtering but no heavy popping, again like it's starving for gas. I could only go up mountain in 2nd gear, otherwise it lost so much power it threatened to stall. If I feathered the throttle it would run smooth, so long as I didn't ask too much of her. Going back down mountain I could get her to do 60 in 5th, no more.
When I resurrected the 83 XVZ years back it had similar symptoms; that turned out to be the ignitor/ECU, which was thoroughly corroded inside. This one is acting similarly. At idle it sounds like a Harley, but I've verified spark on all four coils and plugs. New fuel filter and S-hose, fresh non-corn gas. New float bowl gaskets but few other seals available from Yamaha. The float seats were all loose in their receptacles; I found two o-rings in my stash that worked but the other two are original. New intake boots, replaced the cone filters with an OEM unit and filter(maybe I should check the jet sizes since the PO had cones on it?). Fuel pump was clogged with varnish but I got it pretty clean, and it seems to be pumping gas.
One other thing, sometimes when I put the side stand down it'll quit, like it's in gear and the SS switch is sensing it. Today it refused to restart until I put the SS up, then it stayed running with multiple swings of the SS. When this happened, it would crank and fire but not run till I put the SS up.
Clutch switch is bypassed, fuel indication is bypassed, both at owner's request (lack of funds). That's the story, thanks for any insights.
Richard