2011 115hp loosing power after about 1/2 mile cruise

[lik2foot]

acts like fuel starvation, will still run at and just off idle
new spin on fuel filter and new water separator filter
clean fuel in the separator and the filter looked new that I replaced
engine is on a G3 1966 with approximately 25hr run time

[99yam40]

do you have gauges that are telling you anything?
I am guessing this is a F115, is that correct?

[lik2foot]

correct, fuel gage only

[99yam40]

monitor fuel pressures to see if it is running out of fuel

test and make sure the alarm system works

most have gauges that will give info on what is happening with motor
overheat, low oil pressure or even high pressure, and maybe even other problems

[boscoe99]

What is the primer ball doing? Staying full of gasoline or getting flatish?

[lik2foot]

primer gets flatish, not hard as when pumped up and must hold primer ball just so to get it full of fuel

[cousinabe]

primer gets flatish, not hard as when pumped up and must hold primer ball just so to get it full of fuel

If the primer ball is collapsing, there's a restriction from the primer ball to the fuel tank.
Could be a clogged gas tank vent, maybe mud wasps clogged the vent. try running with gas cap loose.
Could be a check valve,
Could be the primer ball too.