Another prop question!

I have a 1991 Alumacraft Dominator(tiller)with a 1991 Evinrude 40hp.At WOT I’m only turning 4600 rpm.On the boat now I have a 12.25×15 propeller,I want to get my rpms up.I’ve moved the motor up one hole,the compression is 110 on each cyl.so I know the motor is good.I also have it trimed up to the point of bouncing.My hole shot is good,my question is by going down in diameter(say 1/4 inch)and droping my pitch to a 13 is it possible to gain 400-500 rpms?Does any one else have a similar setup,what do you get for rpms and finally what size prop are you running?Sorry it was so long winded.

general rule: 1″ difference in pitch = 150-200 rpm difference at WOT…. so dropping the pitch from 15 to 13 should increase WOT by 300-400 rpm…

Maybe if I move it back to the top I might get some more input.

JJ

Hi this is Joe from Als Specialty. You could have maybe 3 items to check since your compression is the same on both cylinders. A) Maybe the tach is not set correctly for your motor. Should be set on 6 pole. B) Or the throttle is not opening up all the way. C) And a main jet could be plugged on one or both cylinders. D) put on a dyno to findout if it has the proper power!
Just some ideas!

Joe,
I figured out my problem with my low RPM’s.I purchased a Tiny Tach to verify my existing tach on my boat.It turns out my tach was reading 750 to 800 rpms low.With the Tiny Tach it shows that I’m turning 5400.Thats right towards the top end of recomended rpms.Those tiny Tachs sure are slick,it beats taking it in to a shop and dropping 100 bucks to check out your rpms! Thanks again for your input.

Jim