I just bought a new prop because i wrecked my old one. The old one would blow out when i trimmed the motor up so when i bought the new one i got a cupped prop same pitch. Now the new one is worse than the last one. I don’t have a tachometer on the boat so i don’t know what the engine is turning but some idea’s would be helpful on what i should do. Right now i have a 19″ pitch prop on a 90hp motor with a 16′ lund.
Does your new prop have holes in the hub? If so, put plugs in them.
I’m dealing with my own cupping issues right now as well. 
what hole is your motor mounted in?
sounds like it is to high to me if U have a cupped SS prop
There is no holes in the hub and its on the second hole from the top, the cavitation plate is sitting even or just below the bottom of the boat. The prop is aluminum but i guess it wouldn’t hurt to try dropping the motor that last little bit either that or i need a bigger pitch prop idk but it has an awesome hole shot with a 19″
What motor is this?
Dont go higher pitch if you want more RPM, it will lower your RPM (harder for the motor to tun that steep pitch). If you drop down to 17 pitch you will get more RPM (easier for the motor to turn the lighter pitch)
Go pick up a digital Tach and test it. They are about $30.
Every prop performs differently, and may require some other changes. As mentioned, having a tach and knowing the RPMs is critical to the over-all. When buying a prop that has more “cupping” is great. It can actually throw much more water than mickey-mouse ear props. But the Rake is very critical as to how or where it throws the water. Ecspecially in heavier boats like bass or walleye rigs. Having a rake angle that throws the water upward is much more efficient than straight back. However, the motor height must be adjusted to compensate for the rake angle. The steeper the rake angle, the more you want to drop the motor down. Props with a minimal rake will need to be raised up.
I’m assuming right now your spraying a rooster tail up into the air?
No its actually not spraying anything it starts to blow out before i can get it trimmed more than half way
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what hole is your motor mounted in?
sounds like it is to high to me if U have a cupped SS prop
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Go pick up a digital Tach and test it. They are about $30.
This is very good advice. Trying to diagnose propping issues without knowing your RPMs is like trying to do a paint-by-numbers with your eyes closed. A cheap digital tach can be installed in less than 30 minutes and will give you the info you need to make your next move to get your prop figured out.
Looks like i’ll have to invest in a tachometer, that and try dropping the motor down that last little bit
If you don’t want to mount one you can just buy a non permanent one. You can get a good digital one for about $40. It will hook up to your motor and after testing you can take it off. You will have to have your cowl off while testing, and if it is not a tiller you will need someone in the back to read it while you run.
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