[wildbill]

earlier bikes have that red undercoat paint or whatever inside the tank. this as been know to flake and block the pump. I think its more of a replacement then than a fix.
if you pulled the tank and dropped all the fuel or drain it out -you might be able to see if its contaminated in the fuel or not
not a problem with mid 015 onwards as its a new style tank and no paint inside the filler

[Ice]

My experience with these bikes has shown that they truly are dead simple, more reliable than people think, but do have a few quirks.  The nice thing is you CAN work on these yourself and sort stuff out if you want to.
I think one of the most overlooked "issues" that most folks have is shit fuel - typically water in the fuel.  I've worked on a few friends bikes that had - intermittent "issues"; drained the tank, added high quality fuel and problem solved. 

Run it for a while like it is to see of the problem is solved- you may be pleasantly surprised.

+1 !

[suitcasejefferson]

Uh, have you considered the CDI? They don't fail very often, and when they do they usually fail completely, but not always.

There are 2 carb kits for the B5, both use an Amal carb. I kind of wanted a Mikuni, but will likely go with the Amal. Yes there are a lot of exhaust options, but finding one that looks like it belongs on a vintage British bike is not as easy. I like the Triumph "peashooter" style, which is very similar to the EFI pipe. I may just go with that one.