83 8 hp seahorse overheating, exhaust exiting water indicator. After 5 minutes of operation, loss of power, steam coming out of rear of engine. I have replaced head gasket, and checked impeller. It looks to be almost brand new. Lots of back pressure on pipe going to engine if I apply water pressure to it. Could it be that ports are clogged in engine or pipe may be clogged with silt etc. Also, can pipe going to engine be removed without removing engine from support. What should I check next?
