Ron, any chance of mailing me the carb spec card etc. ? The non /R carbs fitted to Nortons don't have the elongated slot / side drain and they do indeed piss fuel into the engine or back out of the inlet if there is any over-fuelling.
It's strange though, I've recently put new Amals on my Commando with no problem at all when tightening them up, but the B25 couldn't be done up at all without nipping up the slide. A spring washer under the nut or a blob of Wellseal on the thread helps to stop it working loose without it being tight. Loctite could end up undoing studs when getting it off.