225 Yamaha power loss

[Wiscbw]

Recently, my 1997 EFI 225 Yamaha Outboard has lost top end power. The motor was purchased used and installed this year. At install it would run 5500 RPM,
with a top speed of 52 mph. After a few months of use the top rpm is 5000 and the top speed is 47 mph. I replaced the fuel/water separator. I checked the throttle linkage, I do not see any reference marks but the linkage looks extended. Spark plugs look okay, tell-tale water seems fine, otherwise motor runs/idles fine, minimal amount of smoke. Any suggestions on what to check next?

 

[rodbolt]

Re: 225 Yamaha power loss

check the VST filter,plug caps and O2 sensor output voltage, and also check for weight gain

 

[rodbolt]

Re: 225 Yamaha power loss

why is it posters refuse to post a model number?
in 97 they made 2 versions of the 225. one a 2.6 and one a 3.1, about all they share is a paint code.
hunting for 500 RPM is tough but needs to be done, if the RPM is off 500 with the same prop and weight as before its an indication something is not right, normally its fuel.
normally its lean
lean burns pistons

 

[Wiscbw]

Re: 225 Yamaha power loss

Thanks for the comments. The motor is an S225 TXRV (OX66 3.1 ) I will check the items listed, where is the VST fllter?

 

[rodbolt]

Re: 225 Yamaha power loss

in the vst tank attached to the high pressure pump,
the 3.1 EFI was a very good motor but if the fuel system degrades it is known to pop #1 piston.

 

[Wiscbw]

Re: 225 Yamaha power loss

Rodbolt,
I cleaned the O2 sensor ( it had some carbon buildup)
I cleaned the VST filter in acetone )it also had some crud), and replaced the overpriced vst gasket. Neither part was very bad and the RPM stil only goes to 5100. The max thottle position sensor voltage is only about 4 volts, is this too low? Thanks for your help. should I replace the low pressure fuel pumps next or some other filters?

 

[rodbolt]

Re: 225 Yamaha power loss

4V is about right, test the stator and pulser output voltages, each stator charge coil power one bank of ign.
the fuel rail pressure is easy to test.
the injector filters and the pressure regulator filters are easy to test/check.
has the hull gained anyweight since purchased ?