40 mph but gauge only showing 1400rpms on a mercury 2005 4 stroke 115??

[polar115]

At WOT I am getting a reading of 1400rpms at 40mph. Motor runs great and no problems but not sure why I am getting this reading on my rpm gauge. I have a 19 ft Polar with a mercury 4 stroke 115 2005 model. At idle it reads 750 rpms but when I give it gas it only goes up to 1400rpms but runs at 40 mph. Any suggestions?

 

[ONERCBOATER]

Re: 40 mph but gauge only showing 1400rpms on a mercury 2005 4 stroke 115??

is the tach set for 4 cyl 4 stroke? (i assume 4 cyl) if it was set for 4 cyl 2 stroke then it would read 1/2 as many pulses and display 1/2 actual rpm. if it was set for a 6 cyl 2 stroke... even bigger dif. I would be suspect of the gauge at this point. Also what is the recommended RPM range for this engine to operate in?

Sean

 

[polar115]

Re: 40 mph but gauge only showing 1400rpms on a mercury 2005 4 stroke 115??

I need to check the tach and see what it is set for. Do you know how to do this? You are correct it is a 4cyl. Just got the boat and from what I have read so far the range is 750 at idle and up to 6000 but most people get around 5700 at WOT on the same engine but different types of boats and top speed around 40. Thank you for responding.

Terry

 

[ONERCBOATER]

Re: 40 mph but gauge only showing 1400rpms on a mercury 2005 4 stroke 115??

i think there is an electronics/tech section of this board.... you would likely get far better info from them.... I have a feeling it is either the tach settings or the tach itself. the tach should have an adjuster on the back... and it should be set for how many pulses it would sense from the engine... maybe this engines stator has more or less poles than the previous engine.

Sean