My 97 900 ZXI won't go over 5000 RPMs. It was the first time out this summer, BUT the last time we had it out, my dad sucked a rock into the impeller and we had it tipped on its side for a good hour or so to get the rock out, and it never ran the same since... So we replaced the impeller the other day and the engine still doesn't run right, I replaced the plugs, inline fuel filter, and still does the same stuff. Please help me.