05 vz 300 problems

I have an 05 VZ300 its very hard to start, runs good for a while and then looses power at top end and fouls the plugs pretty fast. Have about 85 hours and on the fourth set of plugs. Has the updated oil pump, just readjusted the tps....fuel pressures are good. Dont know where else to look....any ideas? Thanks in advance.

[boats.net]

May have a ruptured diaphram in low pressure fuel pumps. Number 36 in diagram: Yamaha Outboard Parts 2005 VZ300TLRD FUEL Diagram