2002 Yamaha OX66 loss of rpm

[Tripletailing]

Boat struggles to get up on a plane. Eventually does but only turns 3800-4000 rpm. Tried correcting fuel issues by doing the following:
1. Replaced both low pressure fuel pumps, one was bad
2. Cleaned the o2 sensor 2 years ago with same symptoms,replaced it now
3. Replaced spark plugs
4. Replaced VST filter and water seperator filter
5. Ran on portable tank bypassing bulb and pick up tube, problem the same

I ran boat to around a quarter of a tank (+/-20 gallons), lowest in years,before refueling at a marina before troubles began.

Looking for next step, I'm a rookie shade tree boat mechanic!

 

[ARCHSEA BUNKER]

Re: 2002 Yamaha OX66 loss of rpm

what about the filter on the motor

 

[cousinabe]

Re: 2002 Yamaha OX66 loss of rpm

have you cleaned your fuel pressure regulator screen on the vst tank?
you can also clean the screens on the fuel injectors. pull off the fuel rail. on each injector, there is a tiny screen pressed in. gently pull/twist out.

i would monitor both low and medium fuel pressures during problem.