I bought a used 05 Shadow Aero 750 and LOVE it. However I am only getting around 30 to 35 mpg and know it should be much higher. The bike is stock except for the pipes. The previous owner upgraded to dual strait pipes which are nice and loud. Are they hurting my mileage? Also lately I have noticed a lack of response when I twist the throttle. It delays a little then goes. Any help? Thanks.