Hey Gareth,
Harry's bike has had the same issue passing through water when we first got it. At Conondale last year I took the tank out and sprayed everything liberally with silicone spray. Haven't had the issue since.
Re the bogging down issue, sounds carb setting related, Harry's bike was perfect when we got it, I haven't touched the carb or spark plug in 2 years we have had it but it was second hand and likely the former owner sorted it. It took me a while to get my TRS right from brand new....
We can take Harry's apart on the weekend at Hinchies and check all the jets and needle settings if you like.
Cheers,
Jeremy