tfe1870
old650
i am working on 1982 xs650 with 2,600 miles showing. rode about 20 miles and was running perfect when it started loseing power and backfiring thru carbs and exh. made it back home and it would start and run up to about 2000rpm. i changed coil and wires, spark plugs, ignition box, pickup, cleaned all connections, including the connections inside the headlite pod, including switch. had carbs off twice and nothing has helped.checked valve clearance, ran compression check replaced rotor.still starts and runs fine up to 2000rpm. any suggestions what to try next?