Trying to figure out why my motor has lost 300 rpm on the top end.
Motor was purchased about a year ago. Had dealer check my tach and he said it was about 300-400 rpm fast.
Motor propped with a 13" Vegeance on a small gearcase.
As recently as this June motor would turn 34 mph top (GPS) with my tach indicating 6400 rpm. I've done numerous checks to verify over the past year. By the way I'm using the same GPS unit (Lowrance 332C unit)
Running my boat last week with the same prop, very similar water and air temperature conditions, the same boat weight etc. my maxed rpm was 6050 rpm and the speed was 32 mph. My speed at 4000, 4500, 5000, 5500 rpm is essentially exactly the same as it was when my motor would rev to 6400 rpm.
I'm not especially concerned about the loss of MPH as the boat really handles best around 28 mph. And, I'm still in the rpm range indicated by Merc (5500-6000 rpm). The boat gets on plane fast and performs excellently in the mid to upper mid range of rpm.
However, the loss of top rpm puzzles me and so am asking if anyone has any thoughts on this. By the way the boat is set up exactly the same over this time period.
Thanks,
Bob
Motor was purchased about a year ago. Had dealer check my tach and he said it was about 300-400 rpm fast.
Motor propped with a 13" Vegeance on a small gearcase.
As recently as this June motor would turn 34 mph top (GPS) with my tach indicating 6400 rpm. I've done numerous checks to verify over the past year. By the way I'm using the same GPS unit (Lowrance 332C unit)
Running my boat last week with the same prop, very similar water and air temperature conditions, the same boat weight etc. my maxed rpm was 6050 rpm and the speed was 32 mph. My speed at 4000, 4500, 5000, 5500 rpm is essentially exactly the same as it was when my motor would rev to 6400 rpm.
I'm not especially concerned about the loss of MPH as the boat really handles best around 28 mph. And, I'm still in the rpm range indicated by Merc (5500-6000 rpm). The boat gets on plane fast and performs excellently in the mid to upper mid range of rpm.
However, the loss of top rpm puzzles me and so am asking if anyone has any thoughts on this. By the way the boat is set up exactly the same over this time period.
Thanks,
Bob