I bought a couple of used 6080 from the selling forum and when I put them in the water they turn on but no water movement at all, they click and shake, and I see the prop turn but not smoothly it seems to jerk and run at various speeds. I took the prop out and made sure there was nothing to jam it up and it looked clean. I was told they were working great when I bouth them? What could be going on and can they be fixed for cheap?