1970 merc 9.8 110 rpm check

[tacx]

I have the above engine and have gottin it running great, but I don't think I am getting the the most out of my top end wot. How does one check if the engine is running at its maximum rated rpm?

Thanks
Tom

 

[tpenfield]

tachometer. There are optical and inductive ones that can be used to check it. I was thinking of installing an inductive tach on my Merc 7.5 hp.

 

[RCO]

I use a generic version of the "tiny tach" on my smaller outboards. It is within 50 rpm of my snap on optical tach and a lot easier to use on the water.

 

[tacx]

Thanks guys.
I have an optical tach that I use on my rc plane engines. Just point it at the running airplane prop and check rpm.
But how would I use that on my outboard? Point it at the flywheel.
Also, how does a inductive tach connect to the engine?

​​​​​ Would any of you know off hand what would be the wot rpm for my engine?
Thanks
Tom

 

[RCO]

To use an optical tach you need to paint a mark on the flywheel. The tiny tach has a wire that you wrap around one of the spark plug wires. No cutting out splicing needed.

 

[tacx]

I don't relish the thought of going across the water wide open and trying to hold a optical tach pointed at the spinning flywheel. . I can only turn the throttle past idle speed when the engine is in forward gear.

So, I think an inductive would be a better choice. I will research "inductive tach".

What about my other question regarding the proper wot rpm for my motor?

Thanks
Tom