F50 won't reach full RPM at WOT

[<Dan B>]

Will reach full RPM at WOT using idle control lever (i.e. not in gear, in my slip), but out on the water (with gear in forward) - will only read 4300 RPM at WOT. Manual shows should hit 5000-6000. Changed prop to identical ones used by many with my same boat - got me up from 3400 max to 4300 max by installing one with lower pitch. I am now at the lowest Yamaha makes for my outboard.

Any ideas?

[<boats.net>]

You might have your dealer check it out, it could be improper tach reading, engine not running right, or the motor installation on boat. You shouldn't rev motor that high with no load on it, it can cause serious damage to engine