Keeps cutting out....Petcock or vacuum.? XJ650

Hi gang,
Cant figure this one.
Recently she felt like she was running out of fuel so I switched onto reserve but she still cut out. I have an inline filter and can use it as a window. So on advice I ran her on prime and bingo.. No issues. So I bought the petcock repair kit and installed it using BigFitz's excellent step by step guide. I thought the problem had gone away but this morning I switched her to res and she died on the road. I could clearly see that there was no fuel in the filter. Put her back on prime and took a while for the fuel to flow. Now..the tank isn't very full at the moment. So I tilted the bike over to the petcock side and could see the filter filling up even though it was at a trickle... I am now just thinking of buying a new petcock. I hear that the repair kits dont always work.
But... Is there any other reason why she keeps cutting out like this.?
All help is appreciated.
Morg

 

If it wouldn't flow but a trickle even on PRI, I'd suspect a plugged gas cap vent.

 

Thanks BigFitz.
So this means if I open the gas tank I should see a stronger flow.?
Where is the gas tank vent so I can check it out.?
Could it be a blocked vacuum hose either.?
Thanks again,
Morg.

 

-Yes.

-It's "built in" to the gas cap; take the cap apart and see how corroded it is internally. Clean.

-Yes it could be a blocked (or cracked) vacuum hose. It could also be a non-vacuum hose used as a vac hose and it's caving in on itself under vacuum once hot.

 

And from only moments ago, if this is the problem
http://www.xj4ever.com/gas%20cap.pdf ..pizza optional