'85 Merc 60hp - Tach Question

I have an '85 Merc on my '81 16' Lund Pike Dlx. I starts and runs beautifully. I installed a tachometer in the console when I restored the boat.

The tach appears to work well at lower motor RPMs. Idle out of gear at about 1200 RPM, idle in gear at about 800 rpm. And appears to track the motor RPM up to some where about 4000.

As I increase the throttle position above that position, engine noise would give me the impression that the RPM is still rising.

At some point above the 4K mark the tach pegs out and I loose the RPM information.

This was a project boat so I have no experience with this boat, motor, prop pitch combination.

The prop doesn't appear to be limiting the motor rpm. But I am afraid leave the motor run at wide open.

The tach has scaling to about 8000 rpm, so I would expect it to accurately track to that point.

Now, if I selected a different tap point on my rectifier would that solved the issue of tach readings?

Any input or experiece would be appreciated.

Thanks

Mine did exactly that thanks to an aftermarket voltage regulator. If you have only the factory rectifier, try switching the tach lead to the other yellow wire on the rectifier.

Jeff

Jeff,

Thanks for the input. I only have the factory rectifier, relocate the tach tap before my next trip out.

I relocated the tach tap to the other stater wire on the rectifier.

It resolved the issue, thanks

Great! For the life of me I don't understand why that happens. Perhaps some electronics dude could explain it?

Jeff