I have just plumbed in the fuel pump to my 919 Blade and when I power the fuel pump it fills the carbs, but after a while fuel starts coming out of the vent hoses from the top of the carbs.

I'm not sure whether the original bike had a fuel pump or was just gravity fed.

Will I need to put in a return to tank line, or is there an issue with the carbs?

Should the fuel pump automatically cut out when in reaches pressure?

I am not an expert on bike carb's and pumps...

However I always understood that the pump runs permanently and when the carb' fuel bowl is full the float (inside the bowl) closes a valve and stops the carb' from overflowing; which is what you describe.

I hope that helps - looks like your carb' float is not closing the valve. Maybe it has stuck??

The RRV Fireblade didn't have a fuel pump it was gravity fed.

If you are using a bike pump you should be ok, similar design carbs were used with pumps, if so, it seems you have a float valve issue with one or more carbs.

Any CARBED bike pump will do, they are nearly all made by Mitsubishi.

The accepted wisdom is to keep floats, needles and seats in their original sets, I've had better results just chucking them all in the cleaner and fitting them back together 'mixed up'

The needles are triangular in section, if you polish the edges which contact the seat bore it will help, they stick easily and even a bit of surface debris, like dried up stale fuel residue, will cause sticking.

I have an RRV and have a honda fireblade fuel pump and the system will pump until it hits pressure and then stop. I have been running for years with no fuel return and it worked fine, but i have now put a return in.
Having left the car standing for 5 years I have had issues getting the float needles to seal correctly When I measured the floats one was sitting far too low and all of the rubber tips of the needles had taken a set. I replaced the partsand gave it all a really good soak and clean and it came good after a couple of tries.

Sounds like sticky float valves to me. Clean them up and check the float height. Bike carbs are very forgiving. Mine are at a significant different angle to the bike they came from and still work perfectly.