aallhh43

Installed new prop at end of last season. Noticed that now my RPM (Mercury tachometer)readings are off and that to proceed at normal top speed, my tachometer is reading above 7k. RPM's are off by about 2K RPMs. Any ideas as to cause, is it the new prop that is a problem? I purchased the recommended "Black Max". I do not want to return to repair shop and simply open my wallet. Thank you

Gripnriprod Loc: Concepcion Costa Rica

Not likely that a prop change made your tachometer read the wrong RPM. Put your old prop on and check your RPM.
My guess is your new prop is a different pitch.

aallhh43

Thank you!

Fredfish Loc: Prospect CT.

Yep sounds like the new prop has a lower pitch than the old one. Running an under pitched prop will cause over revving and engine damage. Proper pitch will allow W.O.T. to fall within the recommended RPM range, as listed by the manufacturer.

aallhh43

Thank you. I guess I'm back to the marina/boat supplier . . . I wrote Mercury Motors relative to this problem, however, no response/help.

bottomcoon Loc: Tahlequah, oklahoma

Hello43. I ask my service manager about changing props. I have a merc Pro XS 200 hp bought last year. He told me that my computer was set for that prop & any prop change would require reprogramming the on-board computer. I was instantly happy with my prop. After the breakin period on my engine at full throttle my tach showed 7100 rpm's. At my 1st maintenance check I mentioned the high rpm's. A simple flipping of a switch on the back of the tach fixed that problem. I'm now showing 5700 rpm's. I certainly hope you get your problem ironed out quickly.

Fredfish Loc: Prospect CT.

If you were just replacing a damaged prop, it should be the same diameter and pitch as the original. If you are looking for more speed, or lift you can go up or down a little on the pitch, but not a lot.

The number in the middle is the diameter, the last number, with the P next to it is the pitch

Ben Bragg Loc: Dayton Ohio

I’m having a problem getting above 5200 RPM at WOT.
I don’t run this condition much but I’m rated for much higher.
I’ll have to check with my vessel view next time I’m out. See if vessel view matches dash tach.

Fredfish Loc: Prospect CT.

Hey Coon, did you buy a new boat, or repower? Is that 200 one of the new V-8s, how do you like it so far?

OK John Loc: Oklahoma City,OK

Get VesselView. Don’t trust the dashboard tach.

bottomcoon Loc: Tahlequah, oklahoma

Hi Fred! It's a new boat & motor. Yes, it's a new V8. I posted wrong a bit ago, I stated I bought it last year but I've had it 2 years. The first year we experienced flooding & I had a time getting in the water trying to get breakin hours on it. I pulled it to Ontario in September the 1st year & all I can say "it was a trip". I'll take my smaller boat if I go back. Pulling that 108 inch wide beast through those big cities like Minneapolis is not for me. The V8 is extremely smooth & responsive. I don't fully understand the system but it had digital steering. I've had other power steering boats but this is a little different. It's just smoother. I was going to have a kicker motor installed as 2.5 mph is as slow as I can get in an idle. I don't troll a lot but when I do I need to slow down. So far my 36 volt Minn Kota Ultrex trolling motor has been adequate. With spot lock it's really been good. My wife won't let me fish for catfish in it because she doesn't want catfish slime in it. If we ever have a meet & greet I'll bring it along. Maybe we will be back to our original lake in Kansas.

Fredfish Loc: Prospect CT.

That's great Coon, got any pictures? If the tach was always reading high, it was probably set on "6cyl ",since all the motors that size used to be V-6s. I'd love to see it!

jigginjim Loc: Buffalo, Minnesota

Watch clips on YouTube about which prop is for you. Not know the boat you are running, or what the first prop was to what the next size is. I would like if you wanted to pull skiers or tubers, the current prop would give you a
better take off. if you are looking at top end speed the higher the pitch the faster, but that can also limit how your
blast off is. tilt trim is also a item on how your boat runs.

aallhh43

Thanks much. I am working with my prop installer to fin d a fix...

Gripnriprod Loc: Concepcion Costa Rica

Please let us know the outcome. Thanks for posting.