OB RPM Question

[augnmike]

I recently had my 2000 40 hp Tracker Mariner (mercury) outboard serviced to begin my fishing season. The motor is marked that max RPM's is 5500 and in the 12 years I've owned it 5500 is what it has done at full throttle and full speed. Since having the tune up done though it runs full throttle at 4800-5000 RPM's but still gets the same top speed. Do you guys have any idea why it changed? Also does it really matter?

 

[82rude]

If your 100 percent sure about the speed it might be that your tac is wonky now.

 

[roscoe]

Still using the same prop?

 

[augnmike]

Yes same prop, don't know if tac is now off but it would be a coincidence that it went bad right after getting it serviced. So as far as you guys know there isn't anything else that could explain the outcome?

 

[dingbat]

Props move the boat distance x per revolution. Physically impossible to drop rpm yet maintain the same speed.

You are now badly over propped if your rpm has really dropped that much.

What size prop are you running and what was your top speed?

 

[robert graham]

Any changes to that small slot- headed screw/switch on the back of the tachometer?....maybe move it back and forth with a small screwdriver with motor running to try to get an accurate reading(5500 max)......if your motor is obviously running normal and well then must be an inaccurate tach reading......

 

[augnmike]

I am running a 14 prop which is the prop that I have used for years except when at altitude and I switch it to a 10 but I have not been at altitude this season yet so it's got the 14 on it.

I will check the tach screw mentioned, thanks

 

[QBhoy]

Must surely be the tach I’d prop hasn’t been changed and same speed. You would notice a huge drop in speed if the rpm were genuine