I have begun to get a significant decrease in mpgs the last few times i have ridden. I usually get between 55-60 mpgs, but am now getting between 44-49 mpgs. The bike has about 5100 miles on it. I have never had the valves checked/adjusted. Do you think this sudden decrease in mpgs could be due to the valves getting too tight? The bike seems to run as good as ever and to have plenty of power, just is eating much more gas. Please advise.