One thing I once did one one of mine was to install the primer plate so the horizontal line was slightly off horizontal. That is, make the line horizontal like normal, then turn very slightly anticlockwise. not sure if it was the slight angle that made the needle not stick (gravity pulling it slightly sideways then down) or if I was lucky. Ran as normal. I didn't want to go the other way (clockwise) as It might lower float level too much.
The other thing I was thinking of a few months ago was a bit of valve lapping compound on a cotton wool bud/q-tip and using an electric drill to spin the q tip. Maybe this would remove any metal swarf from the brass seat, or plastic swarf that might bind the sides.
