I don't have a haynes manual for this bike but if it follows the usual arrangement for bikes of this era, fuel is delivered to a common rail where the injectors prevent the fuel from entering the cylinder until a small electrical pulse operates the solenoid within the injector. The pressure of the fuel in the common rail is typically around 2.5-3 bar but this acceptable pressure is maintained by a fuel pressure regulator which is attached or is an integral part of the common rail, it's job is to return fuel back to the tank if the pressure gets to high. Inside is a spring operated piston with a needle that sits inside a valve and also controlled by a diaphragm that is operated by a vacuum. Fuel delivery is a fine balance and even a small leak at any of the vacuum lines can cause all sorts of problems including response lag, erratic idle, poor pick up etc. Again I can't be sure of the exact lay out of the fuel delivery on this bike ( I really must get a manual ), but lots of the sensors that send signals to the ECU rely on pressure variation. If you do decide to check the vacuum lines be meticulous, even a small crack at the end of a line can cause a poor vacuum. I hope you find a solution.