Yamaha. Hpdi not running good.2002

It starts and runs . When I power up the motor after a about a few min it starts to drop down in rpm's and run like ****. Like its got a fuel restriction issue. . I have cleaned the vst filter and replaced it at least three times .i put a pressure gage and the vst tank reads 80 psi while running and never drops down in pressure . It acts up but every time I turn the key of for a min and restart I can power back up again . Boat runs and gets up to good rpm's and starts to drop down again. My mechanic seems to think I need to replace the vst fuel pump. I have already done the fuel pumps . I'm wondering if it might be the vst pressure regulator ? We had the computer read it while running and only at certain times did the hpdi pump drop in pressure . But then I can turn key of and power back up.

I had that problem on my 2002 oxy 250's. It turned out that I had picked up some debris in the fuel tank and when I powered up it would do like you described. Cleaned the fuel system out and all was fine. Do you have in line filters? If so, check for debris in there also.