You may have a blocked tank filter in the tap, have you taken the feed pipe out of the fuel pump and checked that you have a good flow?
It could also be the valves in the lift pump and you may need a replacement pump.
The throttle needs to be about half open to get the cold start to stay in. Try moving the stop control backwards and forward, this may release the excess fuel (cold start) button, they sometimes stick and this will stop fuel flow to the injectors when trying to start. Try pulling the excess fuel button with a pair of pliers at the same time as you move the stop control.
It is also possible that the rack in the pump has stuck. Clean around the side plate on the pump carefully, then remove the side plate and try moving the rack that moves the delivery valves with a screwdriver.
May be teaching my grandmother to suck eggs, if so, my apologise but you do know that you cannot bleed the injector lines by pumping the primer pump? You can only use that to get air free fuel to the filter and injection pump bleed screws.