It's hard to tell without knowing which engine you have, but here's something to look into that baffled me for months on my '98 278 Vista's starboard engine. I had similar symptoms - always started at the beginning of the day, but after anchoring for a few hours, it would start, but sometimes die while idling out of the cove or it would die while getting on plane. It would start back up but it got to the point where it was always starving for gas. I replaced the fuel pump with no success.
It turned out the check-valve on the fuel tank had a little varnish build-up around the ball (by that I mean a sliver-sized ring around the ball where it seated) inside the valve, which would make it stick and therefore not let enough gas through. I cleaned it and it has been fine for two seasons now. If yours has this check valve, it's the fitting that the rubber fuel line clamps to on the gas tank.
It may not be your problem, but it's pretty easy to check.
Joe
_________________
USCG 50 Ton Master Inland/OUPV Endorsement+Towing
1998 278 Vista - Twin 4.3 GLs, Kohler 4KW Gen, AC/Heat.
1999 Yamaha Waverunner SUV
2003 Yamaha Waverunner SUV w/MR-1 HO conversion
