Prop Help

[Tennessee Trey]

I have an older Starcraft 1436 mated with a 1975 Evinrude 9.9 that I recently converted to 15 hp with a Carb and a Boysen Reed kit. The boat itself is a bit heavy as I have decked out the front, carry 2 batteries, have a live well and travel with a bit of gear. Right now I have a 9.5 x 10 prop on it that at WOT attains 4000 rpm. From what I understand I should be topping out somewhere between 5500 and 7000 rpm for this engine to attain it's maximum HP.
What I want to do is try some different props with it until I find the one that gives me the RPM I need
Specifically 9.25 x 7, 9.25 x 8, 9.25 x 9, 9.25 x 10.
Here is the problem. I just can not afford to purchase all of these props to test them out.
I was hoping that perhaps some of you may have these props and would be willing to lend them out for a short period so I could test them.
I would be happy to pay the shipping to do this and your help would be greatly appreciated.

[clfarms1]

I would check my tach and make sure it is reading right for one thing. If you drop to a 8 pitch you are only going to pick up 4-5 hundred RPM's and the the light bit less in diameter isn't going to make a difference. I looked and a 9.9 wot is 5-6000 rpms, and a 15 is 5500 to 7000 rpms, I don't know is just changing the carb and reed kit will change it that much or if you have to do something else

[Tennessee Trey]

The only difference in that years 9.9 and 15hp is the Carb. Everything else is the exact same motor. It is a very common conversion.
Pretty sure my digital tach is reading right.

[Cray]

Where is cavitation plate on motor in relation to bottom of boat? Like Steve said going to be awful hard to reach RPM you want with those prop sizes if motor is mounted right on transom and Tach is right. Usually one in of pitch gets you around 200 rpm.

[Tennessee Trey]

Cavitation plate is about 1.5 inches below the bottom of the boat.

[Cray]

Trey, just a suggestion you might try. If you can put a spacer on top of transom to lift motor to where cavitation plate is even with bottom of boat. Run it and see what that does for rpm. If that helps might want to build a permanent lift that sandwiches the transom and gives you support on the top.

[Tennessee Trey]

I think that sounds like a good idea. I have been wanting to build a mini jack plate for it. Now just might be the time.
Thanks Cray!
I am just trying to tease the best I can out of this little rig.
Found the boat in the bottom of a cattle pond a few years back and have redone it.
Rescued this motor for it from a pile.
I want it to be as good as it can.

[Bassing_53]

maybe try to trim the motor different to match the weight in boat. there is a rod that the motor rest on when in down position. pull it out and try a different hole