If your timing belt is off, there is no way to adjust the ignition timing to correct for it. Adjusting the distributor only adjust spark timing. The timing belt keeps cam lobes timed up with the crank/pistons.
If it is in fact running rich, it could be the ECU dumping to much fuel in the intake, which can happen at low rpm, especially if the engine is cold or you have changed the cam or if the ECU has detected a problem. It could also be a malfunctioning O2 sensor.
Just my
