Putting a Remus can/Y piece usually leans things up a bit.
If the rich running has only occurred since you fitted them,the most logical source of the problem is with the work carried out.
The O2 sensor/lambda probe thingy (which controls the mixture setting to a degree) seems the first thing to check out,but you should also search on "Cat code plug"(i believe this changes the ECU mapping to compensate for different conditions) and Throttle Position Sensor (TPS) adjustment (this affects the amount of fuel gobbed into the motor).
Also try removing F5 (for about 30 secs)to reset the ECU and then ,with the ignition on,motor not running,fully open and close the throttle a couple of times to allow the ECU to "learn" its min/max setting.