Acetone was by far the best. Melted the carbon deposits away. I tried several degreasers and Acetone was by far the winner. For the swirl flaps you could literally submerge them in Acetone and then just using a brush agitate the deposits away.

As for the manifold I just poured Acetone in it and let it set for a while upside down on my bench and then worked it with an assortment of brushes I got from Harbor Freight. This was after I submerged the manifold for 2 days in simple green commercial grade degreaser. This combination seemed to work pretty good.