I recently picked up an older raleigh conversion, it rides great execpt that the chain comes off randomly every 2-3 miles. And whats weird is that it never has happened under hard acceleration, it is always when im pedaling very lightly. The chain alignment seems to be pretty strait, maybe an 1/8" of an inch off in one direction. Is that the cause of the problem or is there another issue im overlooking. Thanks for any help.