i had the same issue with an older 120 and seen the malkings for the same problem on my inboard 454. the impeller had come apart in my 120 and a chunk of it had made its way up the intake hose to the elbow that goes into the side of the engine i took the intake hose off quick as the engine was running to check for water flow and the rubber peices were jammed in the elbow. my 454 had the impeller come apart with the previous owner and the chucks were stuck in the tranny cooler inlets side. hope this helps. good luck