I replaced a bad impeller in my 4 stroke 15 hp Yamaha not long ago,tested afterwards and had plenty of flow.On a recent fishing trip,water flow stopped completely. I removed and inspected new impellar,it is fine.I also removed discharge hose inside engine compartment and can blow through it with ease,also rinsed foot with fresh water until water flowed freely.Re-assembled and still have no water flow.Any suggestions?