Check out Dawn Power Dissolver. I used it on a muffler and documented the results here:
[link=http://Dawn Power Dissolver]http://www.rcuniverse.com/forum/fb.asp?m=5929584[/link]

Some have said not to use it on aluminum parts but others say they have but to brush it off after 3-4 minutes.

What I like about it is that it is quick, (squirt it on, wait 3-4 minutes, brush it off, wipe off engine) non-toxic, and does not require a crock pot or rice cooker.

The results speak for themselves.

Whatever you decide to do, good luck!