Lower RPM's on Yama 150

[OZ WHITE]

Put my 204 overnighter with a 2016 Yamaha 150 (80 hours on motor ) in this weekend...only getting 5300 rpm ....3 months ago was topping out at 6000...it was stored with a full tank of fuel and Chevron Techron Marine additive...Any ideas as to the drop in RPMs..sill getting about 34 mph...but why low RPM

 

[Halfhitch]

Was it setting in water that 3 months. Dirty bottom maybe? Did you trim up on plane till the prop blew out, then back down till it bit, or was it tucked in? Did you have full enclosure up recently and down 3 months ago?....Just some things a person that wasn't there would wonder about.

 

[seasick]

It makes no sense to me as to why you would get the same max speed but at lower revs. Now if the prop were slipping last season, I could see a reason but not the other way around. That would mean that the prop sliiper before but not now and that is usually not how things go. It seems that some factor is different as Halfhitch alluded to.
How did you measure the speed?

 

[OZ WHITE]

Thanks for replies...top speed was actually about 5 mph lower than at 6000 rpm (sorry for the wrong impression.)..didn't spend to much time or attention to getting the trim right..thanks for the clue half hitch....

 

[wrxhoon]

If the engine is running 100% then weight, trim, current, wind and aerodynamics all play a roll and all of them together can explain the 700 RPM drop. 5 mph drop in speed at 5300 works out same prop slip as 39 MPH at 6000.