Any smoke or crud coming out of the exhaust
I would expect that the engine will rev higher in reverse than in forward due to prop geometry. I presume you are doing these tests while tied to a dock
. If so I would expect max rpm
to be a little lower than redline because the prop and engine are under a higher load when static.
I will further presume that in neutral you can achieve static (redline) rpm. This proves the engine is not being governed to a lower rpm but does not indicate if the engine will make rated hp.
Less than max RPM loaded with no smoke = lack of fuel
Less than max rpm loaded with smoke = restriction or overload
You state that you have had a "lower" than 3600 speed since the new prop was installed. This indicates the prop is slightly oversized for the boat. However, you probably still pushed the throttle to max to get max speed.
What I suspect happened fro the point you changed the prop is that you weren't getting complete combustion at WOT and you have been slowly coking up the exhaust
mixer. It is a slow and insidious process.
You checked "up the tailpipe" but you haven't checked the exhaust mixer.
My two recommendations are
- pull the exhaust mixer and check it
- have the injectors cleaned.