~20-27 MPG '03 636. Something wrong? What can I check? My gas light comes on at 95-105 miles. I have about 700 miles on the engine. Im runing 10w-40 Castrol CTX. Its not a big deal, I can pay for the gas Im just worried that something might be wrong with my new bike that I love. I see that some people get almost 40 MPG.