Yep, it was the pick-up tube in the tank. Couldn't find anyone with a replacement pick-up tube in stock, and wanted to use the boat this weekend, so I decided to go with a new tank rather than replacing the pick-up tube. My tank was 18 years old, showing the wear with some surface cracks, and already not legal in some some states due to ethanol and new regulations (according to the salesman . . . ) New tank is smaller and fits in the boat better, and I never use more than 3 gallons of gas on an outing.
And the old warhorse is running like a top again.
I learned a lot, including how to replace the gaskets and diaphragms in a fuel pump assembly.
I also spent time on the phone with 3 different Yamaha dealers within an hour of home, and have a definite preference for the next time I need some major work done.
Thanks for all the help. Without this site I'd have been at the mercy of my local mechanic--the one I've decided won't be getting any more business from me.