Prop size for a 1970 evinrude 40hp electric shift

[1970evinrude]

Hi guys
I purchased a 1970 evinrude 40hp outboard motor with electric shift. It came with no prop, so I'm using a prop off a evinrude 28hp which works but slips once in a while when under torque
There are so many props out there, just want to find the proper size and pitch that works with that motor.
It's pushing a 1970 14ft-15 starcraft boat.
Any recommendation will be greatly appreciated.
Happy fishing and boating
Joe

 

[racerone]

You are sure that it is not the wrap spring that is slipping ???-----The 28 HP ( 62 to 64 ) used the same props as the 40 HP.----But prop selection depends on the boat and for yours the 11" pitch is what I would start with.--Your location ?

 

[1970evinrude]

You are sure that it is not the wrap spring that is slipping ???-----The 28 HP ( 62 to 64 ) used the same props as the 40 HP.----But prop selection depends on the boat and for yours the 11" pitch is what I would start with.--Your location ?

It’s a starcraft aluminum 14-15ft boat

 

[jimmbo]

We used to use a 12" on our 14ft Skagit(glass), an 11" or 12" would be in the Ballpark

What Oil are you using in the Gear Case?

 

[racerone]

Test mark the prop.-----Need to determine if prop is slipping or wrap spring and forward hub are slipping !