Tach settings???

[leebaileysr]

I have a 1997 150 Mercury EFI on a 20ft center console.. The prop is a 21 laser. A blade on the prop cracked and left me looking for a new prop.. Everyone I talked to said a 21 pitch prop was too much pitch... and asked me what kinda of RPMs it was turning, It was turning 5800.. So with the RPMs in question because of prop size I checked the QSI Tach settings. The back of the gauge read 1=4p Alt, 2=6p Alt, 3=10p Alt, 4=20p Alt. It is set at 3=10p Alt. I believe from what I have seen on the mercury website that it should probably be set at 2=6p Alt. being the motor is a 12 pole 6 pulse engine. Can anyone please verify my beliefs before I switch it to the 2=6p Alt. setting, change pitches on my prop and blow my engine??
Thanks for your input

 

[Barnacle_Bill]

Re: Tach settings???

6P is the correct setting.

 

[leebaileysr]

Re: Tach settings???

I took it out today. Made the changes on the tach to 2=6p Alt... I don't believe it to be correct. It showed me idling at almost 2000 rpm and when I opened up the throttle it went all the way over and pegged out way past the maximum number. I stopped and set it back to 3=10p Alt and I ran it WOT trimmed up. It read 5900rpms and topped out at 41mph... I guess the setting of 3=10p Alt is correct but it does not coincide with anything i have read or heard.. The boat is 20ft Henry O, 150 Merc, 21 pitch laser prop... Should I leave it at that setting and try a different prop or is this prop correct??