piaggio 400 cc scooter refuses to start ?

piaggio xevo 400 cc (08) won't start. the engine spins over really well. suspect fuel starvation due to evaporation. Not used for 4 weeks. Have experienced the same problem during September and the engine started a few days later and is running really well. Have the bike serviced by dealer annually. Does the fuel system have a fuel filter to protect the injector? Alan Deal Kent