I have had the same problem previously with the basic 351 engine.
One thing I learned from the fine folks at Discount Inboard Marine is their trick of the trade for testing the raw water pump for volume flow and, good impeller and housing integrity (wear plate and seals) is to get the engine running and rev it up to about 3k. Disconnect the thermostat end of the hose that comes directly out of the pump. It should fill a 5 gallon bucket in about 15 seconds. I tried this just this evening to see if it worked. Spot on for the 15 seconds, My pump is working fine. I have now eliminated that possibility of an issue I am dealing with. Saved me from rebuilding the pump unnecessarily. Good test. Next step now is to pull the riser from the mainfold and check the flow path there at the gasket. While the riser is off, I am replacing the exhaust hose going into the muffler. Those things are hard to replace without removing the riser. That 3" diameter hose is seriously stiff.
Last edited by Cloaked; 08-30-2010 at 10:52 PM.