oljammer

I have a 17' open bow Renken w120/IO w/400 out drive.It is giving me a bad time.
sometimes it won't get up on plane and it will eventually heat up.other times it will get right up
on plane and run up to3800 rpm,and it will be fine UNLESS I try to open it up.When I do this it will not rev op any higher but it will get hot.If I pull the throttle back to where it is running at 3800 it will again run fine.
1-could this be water in the fuel ?
2-be wrong prop size?
3-HELP ME

ok, so you are running at 3800 rpm, say 3/4 throttle....

you go to full throttle and the only thing that changes is the temperature?

does it sound any different?

verify temperatures - get numbers.
grease your swivel bearing in case the impeller is sucking exhaust gases at high rpm.

sounds like it might be a combination of sucking exhaust into the cooling water, and a fuel restriction, or high blowby from breather to intake limiting power

clean the flame arrester atop the carb and other general maintenance items like fuel filter.
check engine compression to eliminate major component issues.

.yes it does,it sounds like an automobile when you need to downshift and don't,thanks,oljammer

on top of the other checks I mentioned, I might be tempted to tilt the drive up and look in the exhaust hole of the intermediate for anything blocking the exhaust. - look in the drive exhaust housing too