I´m having a problem with my 81 cb650. It´s got 19k on it. I´ll fill the tank, run on the main gas line, and after between 40 and 60 miles it´ll die out. I flip it to reserve, and she´ll pick up and go again. So I´ll go fill it up again, and it only used between 1 and 1½ gallon of gas. Given that the bike has the standard 3.5 gallon tank incl the 0.7 reserve number, I should be able to ride it for a good 100 miles before she dies out. The tank is clean. Had a mechanic change a line from the pump to the carbs. Any ideas? Consider me very mechanically challenged. Please help. Thanks.