Have replaced the fuel pump on my K100 with one from a Peugeot 205/309 Gti as the original had been ' got at' by a previous owner. The new pump has an integral aluminium pre filter with no vent pipe connection. Surfing the Forum the indications are that it was fitted to eliminate pump cavitation caused, I assume, by air. What creates these air bubbles, is it under tank temperature, low fuel levels, vibration? Am I going to see this problem in normal day to day running. 
The pump change is my starting point at trying to eliminate poor cold starting and erratic tickover, it hasn't! so will look elsewhere. John

For poor starting and erratic idle, cracks in the boots between the TBs and cylinder head would be my first suspect.

You can test for this by spaying some starter fluid around them at idle.  If the idle goes up then you have leaks and should replace all of them.

after replacing my boots the bike starts instantly and has a very smoooth idle.
it was terrible  before with hard starting in cold weather and nothing i did would cure the poor idle.
well worth the effort.