Ok, will do the fuel bypass, run it without for a while and see if the problem repeats before I fix the old one. I assume it's for safety/not flooding the carbs with the bike on but not running (I can hear it come on with the key to on)?
It cut out a couple times last night again, this time with the tank nearly empty, so it doesn't seem to be a vacuum in the tank issue. It doesn't happen with sustained highway speed during the day (it's been about 80 degrees pretty consistently), but it does happen when it's cooler at night. I'm able to start it with choke on after about 10 sec (even before stopping, just pull in the clutch, thumb the choke, and start it), and after the second time it happened, I reduced speed and limped home without incident, so flow does seem to be a factor, as does ambient temp. If the bypass doesn't work, I guess it's on to the fuel pump.