Just to finish this thread off, After checking the fuel pump and throttle position sensor and finding nothing wrong I pulled the carbs off.
Gave them a complete strip down and found sand in one and white lumpy stuff in another. Also found my main jets were blocked on the top two!
After a good cleaning and a few scuffed knuckles had her out on the water for a good 3hr spin on Thurs - no probs - YEEHAAA!!!!
At last she ticks over and pulls as she should!
Thanks everyone for their advice - I got a great masterclass on outboard maintenance!