So I just started using the dual extruder to save on filament and my results are horrible. My first print went fairly well however I had a LOT of clumping and melting as the nozzle just sat on the filament while the other end was spinning:
Looks like overextrusion to me… try reducing the flowrate % in the slicing program. 95% works well for me in most cases… but step down by small increments.
Ultimately, you’ll want to check the esteps on the extruders. Speaking of which, make sure the esteps are entered after flashing the dual extruder firmware.
It could also be the color and/or type of filament. Varying the flow rate / multiplier % should help the most. Just be careful you don’t under extrude which could cause problems at taller layers. The filament won’t adhere to the previous layer causing delamination or horizontal cracks in the print… more prevalent with ABS due to the contracting nature as it cools.