the stock aluminum impeller is crap. I have a solas 18-24 and 19-25, and with my mods the 19-25 pushes the ski way better than the 18-24, low and top end. you need a stainless impeller if you can find one. you also need a toploader to keep your pump full of water. Cavitation will make the impeller spin when you give it gas and not go like it should. If I think I am cavitating, this what i do. I pull the pump and inspect my impeller for damage to the leading and trailing edges. if there is damage, I remove the impeller and clean up the edges the best i can while removing the least amount of material as possible. then look at the blades in the pump and clean them up if needed. next i screw the impeller back on hand tight and pick the blade that looks the best and while holding the blade steady, use a pencil to trace the edge of the blade on the inside of the pump. now rotate the other blades around to that mark and see if they line up. usually the trailing edge will get bent. if they are bent, then i decide which blade is bent less and draw a new line if i need to. if a blade is bent, i mark the bent part of the blade with the pencil and remove the blade.( I have only done this part with a stainless blade so don't know about a aluminum) then i put it in a vice and beat the blade with a rubber mallet and use a large adjustable wrench, to tweek the blade until all the blades line up with the pencil mark. if the impeller needed this, i can really tell the difference when get back on the water.