Very well could be the motor is now more efficient and just running better overall. So get a screw driver, and turn the idle screw down a tad on the carb. Go for a drive and see how it does.
Have you timed it with a light? As Ben said, maybe you bumped the dizzy without realizing it and advanced the timing a hair and raised the idle that way. Unless your dizzy is very loose, probably not, but worth checking.