2005 90hp Honda not reaching rmp and speed at WOT

[hizzy]

I recently purchased a 2004 Crestliner 2070 VDC (20' center console) with a 2005 90HP Honda outboard. The prob is the original 15 degree pitch and everything i have read says the motor should be in the 5000-6000 rpm range at WOT. The dealership that sold the boat and motor combo to the guy said they ran this boat/motor combo all the time and the boat would run 40-42mph at 6000 rpm all day with the 15 degree prop. My boat is hitting 4800 rpms and 34mph flat out. The dealership recommended raising trim slowly until the speed started to drop and then back it to the sweet spot which is 34 mph on super smooth water. I replaced the fuel line and filter, made sure the throttle on the motor is actually opening up all the way. The gas tank was 3/4 full when i got the boat so i was thinking maybe fuel octane was low. I added octane booster and topped it off with 93 octane gas. So, with all that said, does anyone have any ideas/suggestions on what might be my issue? Thank you in advance!!!

 

[JimmySJ1]

Might check compression had a similar issue and found one cylinder very low on compression

 

[Sea Rider]

If engine is healthy, check prop, could have a spun prop ?

Happy Boating

 

[2nakiller]

I think the prop you need to reach the specified RPM at WOT is going to be a 13 1/4" by 13P, that is what the dealer put on mine when sold. I changed mine out to a 13" X 15P and am experiencing about the same performance levels as you, about 32MPH at 4800 RPM on fresh water at aprox 2100' elevation, slightly better on the ocean.
boat is similar to yours, 21' aluminum center console.
if your prop was spun you would revving much higher.