Mercury RPM help

[Geardog71]

Just bought a used 2003 bass tracker pro crappie 175. It has a Mercury 50 hp ELPTO 2 stroke outboard. First time out cranks up first try, runs n idles smooth, to my surprise. I had my wife and child onboard just to go for a ride. When at full throttle it maxed out at 5500 rpms just like the serial number tag states it should. Now fast forward to this past Saturday. I went fishing alone and I left the landing and opened it up and looked down, and at full throttle it was showing 6200 rpms. Question is why is this, and will running at 6200 damage my engine?

 

[wired247]

Re: Mercury RPM help

You need to change your prop. Go 2 sizes up.

 

[MH Hawker]

Re: Mercury RPM help

Yes it will and its the weight load difference. You need to re prop or run it lower at the correct rpm

 

[Texasmark]

Re: Mercury RPM help

I see a problem based upon your load. Either you have to swap props every time you swap loads, or back off the throttle when running alone. Nothing unusual about it, just the way these things work. Perfectly normal.

Don't pitch your prop to run alone and then load the boat up with folks. Engine does not like to lug and a good guesstimate is that you will to the point where your engine may just refuse to operate under the load.....called 2 stroke loadup. You are on the back side of the torque curve and things just get worse, not better. I think your current prop is what you want as it has your engine running where they like to run with the heaviest load.

Mark

 

[Geardog71]

Re: Mercury RPM help

Thanks Mark and Hawker. Some people suggest keeping two props on hand. A 14 for loads and 17 for running light and alone. I will say I would like to get the most speed out of the engine that I could without over revving 5500 rpms.