Laurel Mountain has a detergent in it to help degrease,but I would not count on it. The carb cleaner is a light hydrocarbon and leaves some residue. I always degrease with hot water and a detergent on a rught sponge and follow up with a toothbrush and
comet type cleaner.I believe the problem is a light hydrocarbon
layer not allowing sufficient penetration of the blueing soln.