I have a 1971 cb500 with 15,000 miles that has sat for almost 30 years. I cleaned and rebuilt carbs, adjusted valves, set points and timing, replaced plugs. The bikes tank was coated by the po sometime in the past. The bike starts and idles very nice at about 800rpms . I have driven the bike on a few occasions for short trips and it ran okay but seemed to have a lack of power in the 3000 to 5000 rpm range. At 5000 and up it seems to have regained power, but once the throttle falls beneath 5000 it feels like it wants to stall. I got it home and re-checked the valves, carb sync, they were good. The 1 and 4 plugs were black, 2 and 3 looked good. It idles and starts real good. There does seem to be allot of pressure in the gas tank after I run it, I can hear it when I shut the bike off. I had a 1977 550 last year that ran great so I know what it should run like. The problem seems to get worse the longer I ride.
