Thanks.
I’m not very up to speed tbh, I bought this bike to learn, however I bought a house shortly after and got too busy to give it much attention.
I did have the carb all cleaned and reset 18 months ago, by an independent specialist who I was recommended, and it did run fine back then, and last summer. but it sat in the garage not being used at all over winter.
Hence I’m going try and investigate this issue myself with help from my dad, so thanks for the tips!