If you suffer from a high fuel consumption you can check the following items for improvement:
1) Let the Aprilia dealer check your Throttle Position Sensor and idle trim fuel settings( using latest 05 engine mapping). with the axione unit. measure the mixture with lambda or CO probe. combine with throttle synch. takes about 1-1.5 hour.
3) Check the air hoses between the cylinders for cracks and if hose clamps have been fitted, leaking will cause rough running and heavy clutch.
4) Has the fuel pressure regulator been connected correctly (on the motor vacuum and not the airbox)? while engine is running disconnect the hose, cover with finger and feel if a vacuum is present. In my case it was not! afterwards the fuel consumption went down from 7 L/100 km tot 5.5 L/100 km and running a lot better.
5) Suspected faulty fuel pressure regulators can be replaced quick and easy with a Volkswagen regulator (Bosch 028016557) of 3 bars. VW number 037133035
(Advice from H. Lambrechts)