RPM's With New Prop

[Sportdog7]

Ok my 15hp. Johnson has a new 10 X 7 pitch prop and its made a huge difference in the boats performance! Its quickly up on plane but without a tach I just don't know how many RPM's I'm running, short of buying a tach is there any other way to make sure I'm not over revving the motor?? It seems to sound fine but I want to be sure any help on this one?

 

[steelespike]

Re: RPM's With New Prop

Really need a tach to do it right.Also need the year of the motor and the comeplete setup.
Wouldn't hurt to read the stickies at the trop of the page and get as much info as possible to us.Tachs like the tinytach are about $43.

 

[Sportdog7]

Re: RPM's With New Prop

Thanks steelspike, I thought I had read here that there was a way to do it without installing a tach that involved removing the motor cover and using some kind of device that was aimed at the top of the motor? I really don't want to install a tach because I really don't have a spot on the boat to put it.

 

[steelespike]

Re: RPM's With New Prop

There is an optical tach.You apply a reflective strip or dot to the flywheel and aim the tach at the strip and it counts the revolutions. Awkward to do in a boat but on flat water held steady against some portion of the power head it can be done. Be careful, no loose clothing or flying hair.

 

[Sportdog7]

Re: RPM's With New Prop

Are these optical tach's something a guy could rent from a marina?