I recently replaced my impeller last weekend. Before it would not pee with the ears but would with the back flusher. The impeller I took out looked new but I replaced it anyway. I unhooked the hoses coming off each side of the cylinder heads. The starboard side had water coming out but the portside did not. I tried putting the hose on the nipple on that head and it did not circulate or come out anywhere. I'm thinking there may be an obstruction in those cooling jackets maybe? Any suggestions?