1999 yamaha 250 ox66 will not get up to rpm

[BarelyLegal]

This motor has ran great before this and I am at a loss. Took it out a week ago for the after noon with the wife and started loosing power. Could only get 3500 rpm (wot is around 5000, cruise on plane 4000). Came in and my buddy who is a mechanic met at the dock. Lifted the engine cover and noticed the two stroke oil reservoir on the side of the engine was a little below full. He diagnosed it as the motor running in safe mode due to the reservoir not being full and most likely it was being caused by a clog in the filter that is after the low pressure oil pump. Changed it, took it back out and it ran great. Took it to Catalina island, total trip was 110 nautical miles. No issues.

Took the boat back out to Catalina and had no issues for the first 30 or so miles. Ran around 4000 rpm, and ran great. All of a sudden lost power and the motor died. Started it back up and could only get 1600 rpm. Ended up limping back home, motor ran fine the whole way back. 5 hours.

No alarms, oil is full on both tanks, fuel ball is hard. Engine does not sound like it is missing, prop spins freely when in neutral. If I keep it in neutral it throttles up to 5000rpm no issues. In reverse in gear it throttles up too. Any ideas?

Thanks

[BarelyLegal]

The first trip to Catalina I had no issues, the second trip was 3 days later and is when I lost power. Sorry if that want clear

[99yam40]

reving a motor with no load on it is bad for the motor and tells you nothing .
It does not take all of the cylinders to be firing/burning properly to make the RPMs go up with out a load.

Pull your plugs to see what they look like.
compression or leak down test would be a very good Idea after running a sick motor for 5 hours.

If all is well mechanically,check to see if fuel pump will run when you turn on the key

and then monitor the fuel pressures when you fire it back up.

[rodbolt17]

and find a real mechanic, if the motor was in safe mode due to low engine tank max RPM would be less than 2500,the far left bar on the tach would be blinking and the audible would be very annoying.

to test the audible simply pull the stop lanyard and crank the engine.

the oil tank does NOT remain full.

it cycles between the marks all day long.

there is no low pressure oil pump.
its simply a transfer pump that turns on and off all day long based on switch position of SW1 and SW2.

my bet is on a fuel issue.
when was the last lift pump replacement?
when was the last VST filter service?

[BarelyLegal]

The boat is new to me, all I've done with the fuel is replace the fuel filter. Can you let me know what you would recommend replacing and cleaning in regards to the fuel system.

[rodbolt17]

I recommend careful testing by a COMPETENT Yamaha tech. first would be a test run at the failure load and RPM while monitoring fuel rail pressure and using the diagnostic test lamp.

but that's just me.
I prefer a calculated test method using correct tools and my knowledge of how the system works.