When I got back to the slip there was some bloke revving hell out of his jet ski, while it was still on the trailer on dry land!
He then launched, jumped on wearing nothing but a short wetsuit, and went flat out towards the river entrance dodging sailboats as he went!
When I got home I tinkered with he outboard, setting the carbs to thier factory settings, cleaning and adjusting etc. I was sure it was fuel related so I also replaced the fuel in the tank. Motor still the same.
In the end I took the three carbs off and gave them a birthday, They weren't the worst I'd ever seen but not the best either. Cleaned out the float bowls, jets etc blew it all through with carb cleaner and compressed air. Refitted the whole lot and what do you know! Primed her up, and after the third turn of the key she fired up and purred like a kitten!
Just gonna go and try it again in a mo so fingers crossed it is still ok.