Fixing the leaking thermostat housing.......success !
Fixing the spluttering at very low revs.....no success !
Stripped the carbs and cleaned all the bits, re-built and still getting the exact same problem. Soooo, looks like it might be a blockage or air is getting in there somewhere.
Fixing the spluttering part 2............success ! Running reeeeally smooth at low revs now. Took me ages to find the problem as it was well hidden. I'd removed the carbs, again, cleaned and tweaked 'em, again and fitted 'em bacon the bike, again. I was about to disconnect the vac pipe on the fuel pump side where it connects to the engine inlet stub but decided to disconnect it at the fuel pump end this time. Pulled the pipe off and discovered a t connector for the scottoiler. Then discovered the other end of the scottoiler pipe wasn't connected to the oiler.
Decided to blank it off with a screw.
Will connect it to the other vac pipe then I won't get any problems with the fuel pump.