RePowered Boat Tach Question

[GranvilleDave]

I have a 1994 Fisher Avenger that was repowered from a Mercury to a '74 Johnson 50 HP. The Tach is set at 2P/4C and I believe that it is reading about 2x what it should be. THe tach also says that it's for a 4 Cyl Gas OB w/Alternator. My motor is 2 cylinder 2 cycle gas and I assume it has an alternator.

Can I change this to 6P and get an accurate reading or do I need to replace it with a new alternator? Thank You for your input/thoughts.

 

[GA_Boater]

That is a gas 4 stroke IO and 2 stroke OB tach in one. The tach will work with a 6 or 8 cylinder IO connected to the coil, the 3P/6C or 4P/8C settings. For an OB with alternator which is most of them, you have to find the number of poles (windings) on the alternator and set to that number.

I think it's 6, but I'm not a Johnson guy. It won't hurt to change it to 6P until one of the Jonny/Rude guys check in and correct me. I don't mind.

 

[GranvilleDave]

Thanks GA_Boater! That would probably explain why my other thread about prop and RPM is causing a bunch of confusion! The tach readings were wrong.