vfr 400 not getting gas

[el_scor_cho]

hey guys need a bit of help.
my vfr 400cc (1989 nc30) runs fine for a while then seems to starve itself of gas after 5-10mins. almost exactly the same feeling as when the reserve switch on the tank is needed to be switched on. have taken apart the tank pipes etc and all seems to be in working order. although the diaphragm at the base of the tank seems a little worn but still does its job. havent really gone too much further into the bike than this
another thing is that i can no longer let the bike idle without the choke on, or else it revs too low and dies.
this wasn't a gradual thing

thanks for your help !

[vifferman]

Well, it's obviously fuel starvation, and there's a finite number of things to check for this.
Venting: check that the air can get into the tank, otherwise fuel struggles to get out. Vent is either a hose, or in the cap.
Tap: Simple to check - take off the hose, turn tap on, make sure flow is OK.
Filter: Does it have one? Is it blocked? If you can't tell, compare the flow with the filter in place, and with it removed.
Carbs: Are they crudded up, causing the crud to be sucked into the jets after a few moments? Is there water in them? (Both these things can be checked by opening the drain on one or two, collecting the drainage into a glass jar, and examining it). If they're crudded up, you need to clean out the tank, then clean out the carbs.
Mechanical: Is all sweetness and light with the linkages and cables and adjustment?