I discovered today the main cause, a butterfly valve wasn't opening correctly, very stiff due to crap sticking in, looks like water got sucked in somewhere and made a mess. Also my starter motor is knackered, again due to water and salt. I'm out of action until I can get new parts. Still not wasted time as I learnt a lot about my outboard while kieron from ribshop was diagnosing the fault.
Lesson to learn, while playing in waves is great fun, too much of the wet stuff hitting your outboard will lead to costly repairs. Baa humbug.