Fuel pump problem?

So wheeled the old lady (2kr) out this morn and she wouldnt start....cranking over she sounded....different, and the classic fuel pump priming sound didnt happen. Tried to push start her but no go. Tried the on-off switch a few times, occasionally she would do the priming sound, but even then she wouldnt start.

First off I checked the electrics - figured out which were the starter and pump relays, swapped them, and the started still cranked (and both were clicking) - sweet, not the relay. Then I popped off the fuel pump connector and checked continuity and that it was getting power - continuity good and I got the 12V for the 5s or whatever it's meant to be when you turn on the kill switch. (However what I did not do was put little bits of wire on the connector so I could check if power was getting there even when the pump wasnt priming - thats on my to do list...)

So I figure it's gotta be the fuel pump - I read quite a few posts about draining the carbs, off i went to see how much fuel i got out (i dont know anything about carbs, but i like to give things a go- its a good learning experience). Draining one carb i got *maybe* 1/4 a cup of fuel, probably less - not quite the 1/2 cup that was mentioned. Read elsewhere you can just bypass the pump as long as you have enough fuel in the tank (I have about 9L in there atm), so I tried that. Instantly she sounded better when cranking over, and after a heap of cranking and JUST catching then dying I got her going.

Sweet, defs the fuel pump - then i thought why not didnt I just check the pump and see if its actually pumping fuel out when it primes - so I pop the outlet hose off the pump and lo-and-behold its working properly. So I plumbed the pump back up and she fired up first go. (Mind you this was just after I had her running without the pump)

Now I've only fired it up that once, but this leaves me a bit perplexed as to whats wrong - at a guess I'd say the pump is starting to crap itself, but has anyone else experienced this sort of problem? (Like i say, im a rookie at all this.) Kinda dont want it packing up on me in the middle of nowhere... :/ I'm open to any suggestions.