Checking max rpm T9.9 high-thrust 4 stroke

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Is it possible to use an automotive tach to check for maximum rpms on a

[robtag]

Hi
I meant to ask if it is possible to use an automotive tach Snap On with an inductive pickup to check the maximum rpms on my T9.9 4 stroke? I am using the motor on a 28 foot, 2800 lb trimiran. Are people using the stock prop when using this engine as a sailboat kicker? I think that the prop that came on the engine is the smallest available from Yamaha, but I do not get an increase in rpm for the last 1/3 of the throttle travel, and the linkage is moving the throttle plate. However, the fuel economy at partial throttle seems very good.