I got as much info as I could from the internet and literature. I backflushed the water system but although water seemed to pass through OK, the engine still had no circulation.
By the way, never be tempted to forward flush the system with an inverted engine or water can get up the exhaust and into the crankcase.
I tried removing the propeller in case of too much turbulence in the dustbin but no luck. I left the block to soak in a hot solution of Holts radiator cleaner/deruster but still no circulation. I was brave and undid the pinch bolt which holds the prop gearbox assembly onto the shaft housing. I then undid the two top screws (hammer driver required) to gain access to the pump impeller. This was intact, in good condition, clean and not blocked. Then I thought I must bite the bullet and remove the "do not remove" cylinder head.
However, when re-fitting the gearbox assembly onto the shaft housing, I realised that I had purchased a motor which had been wrongly assembled at the last service. The long copper pipe which feeds water to the cylinder block had never been correctly fitted into the pump outlet hole but had just hung down inside the exhaust, connected to nothing. I put it together correctly ( care required to get the pipe to line up ) and hey presto, my pump works like a fire engine.
