5.7 Mercruiser Won't run except higher RPM

[Vanha Pieru]

'97 5.7Mercruiser. Sat for about a year. Started right up and ran fine for a couple hours cruising and skiing. Suddenly got hard to restart, progressively got worse, would start at high rpms but hard to get into gear. Limped back to the dock. Now can not get from high rpm into gear at all; had to crank it all the way on the trailer. Non-Ethanol gas, sat with full tank with sta-bil in it.
TIA!

[mmwjr]

When you say it would start at higher rpm but hard to get into gear do you mean it would start which the shift disengaged by pressing the button in and advancing the throttle? Then would stall when you returned the throttle to neutral to engage the shifter? Have you tried changing the fuel filter?

[Vanha Pieru]

Correct-starts but when one lowers rpm to engage it always dies.
Worked fine for a couple hours than started acting up.
Checked fuel filter in line and on the carb, and fuel pump seems to pump sufficient. Dumped fuel filter and no sign of water in the jar. Odd that it will run at higher rpm but not low. Going to try pulling gas from a can while on muffs

[mmwjr]

I want thinking so much about water in the gas as opposed to debris that clogged the filter. Running on the muffs probably won’t tell you much as there won’t be a load on the engine as when it’s in the water but worth a try to see if it will idle.