2004 150 Optimax Alarm At Throttle

[jollygreengunner]

I have a 2004 Merc 150 Saltwater Optimax, I rarely get to use my boat, but when I do it seems there's always issues. The other day I tried to take it out and it would idle fine for about a half mile out to the channel. When I went full throttle to get up on plane, the motor began to stall, choke down and lose power back down to idle. It could never get on plane. I idled it back to the ramp and it died a couple of times on the way. It typically would crank back up, but the last time it didn't and I had to come back under troll motor power.
I got it back to the house, pulled fuel filters under cowling and on transom, dumped them, ran it clean and dumped them again. Did this for a couple of times. When I was running it in a barrel filled with water at the house I noticed that when I would go to full throttle I could hear an alarm. It would get louder with the more RPM's from the throttle and would die out after a couple of seconds when I throttled it back. I'm pretty sure this could be a overheat issue, but I just changed the water pump and propeller last year and haven't ran the boat more than twice after that. I also replaced the thermostats last year as well. Any ideas to where to look next or to check back over what I've already done. I wouldn't think that the water impellor or thermostats would go out that quick, but I'm no expert.

[boats.net]

Running in barrel at higher rpm's can cause it to overheat, possible from lower unit not being deep enough in water or water intake pulling exhaust bubbles and not getting
enough clean water to keep it cool, May need to test run on water with fuel pressure gauge attached to check fuel and air pressure.