fuel starvation at higher rpm

Hi guys, been lurking for a bit but it seems its time to post.

put my cb500 on the road yesterday after having it restricted, it was driving well and all was well, this afternoon i went to take a longish spin and within 1 mile i started having fuelling issues over 50mph but under it theres no problems atall under 50, basically the motor seems splutter its way down to a stop, sometimes slowing down lets me keep going but not always. when the engine stops i generally need the choke to restart it and the rpm can jump upto 4k at full choke, usually it cuts out full choke.

had a look at the fuel pipe hasnt got a kink in it, the petrol vac pipe seems ok to me too, but it is rather easy to take on and off by hand but it does seem to be sealing if i remove it when the motor is running maybe a tighter hose clip is needed?

when i blow down the vac pipe gently i can feel the diaphgram stop the airflow and when i suck it its just continuous suction with a slightly petrolly taste, i dunno but is this normal, seems like it should be to me?

any ideas/advice would be much appreciated, thanks.

I had this a little while back, and it turned out that the vent on the petrol filler cap was partially blocked and allowing a vacuum to build up in the fuel tank.
Wasn't till I opened the tank cap (muttering and cursing to check I had enough go-juice) and I heard the hiss as the pressure equalised that I realised this. Bike started immediately after this.

A tighter hose clip on the vacuum hose won't do any harm, and it will eliminate the loose connection possibility easily

a mate had my exact symptoms recently on a fireblade and it was dirty petrol, will try running carefully with the cap open first and failing that ill be draining the tank. irish petrol tends to be shite

well i can confirm today that the tank was infact hissing but i couldnt replicate the stalling, and after a while the hissing went away all by itself, bit confusing that but at least i know where to look the minute it crops back up

and now its back :/ guess theres no way around taking the tank off yet.

I have exactly the same problem, but only on heavy rain. The engine just slowly dies. Won't start until I pop the filler cap, hisses, then it works fine.