Just sounds like its running rich. Spark plugs will give you a good idea, as it's still the best way to know for sure whats going on.
Cheers man. I managed to do 165 miles on 25 quid today, around 42.5MPG. Not bad considering I've advanced the dizzy a touch and I was redlining it quite a lot(trying to catch a skatepark session on time), with quite a lot of stop starting, roundabouts and motorways in between, oh and a few hills. Really good test tbh. Think my engine is running pretty good now, powerful too.
Just need to change the GB oil to see if that has any effect
Also the tips of my spark plugs are creamy white colour, all intact and on the whole look ok. I dunno if that beneficial for you @solarice