Rpms on new boat. Tachometer not set right?

[Luedy22]

Hello, just got a new seaark tunnel hull tiller. Decided to mount a sandec tachometer/hour meter on and found that with a 15pitch prop I was only turning 4900 to 5100 rpms. Mercury says they recommend between 5500 and 6000. So I dropped the pitch to a 13 pitch and it is now reading only 3500 when it is jacked and trimmed but still runs only about a mile slower. Is this tach not hooked up right? The instructions were to wrap 3-4 times around 1 spark plug. Logic tells me I'm doing something wrong if when I drop in pitch I drop in rpms as well. Any help would be great since I can't m figure it out to save my life.

 

[bamalivin]

I have installed a mini tach on my 89 Evinrude 20 hp and discovered that I too was over pitched. I purchased the motor with a 10x15 prop and re-pitched to a 10.5x11. I gained about 1k RPM at WOT. That being said you should have gained RPM aswell. Some considerations to take into account: was your boat load about the same both trips? Did it seem like the motor was running well?