I use some stuff called "ZIPP" in the heating trade and tried it in my engines to clean them out works like a charm ,clean and 100% dry, follow it up with some aro and no rust "ZIPP" can be had at your local heating supply house but be mindful it is a chlorinated solvent so keep it away from plastics.
for baked on residue use "grime solve" and rinse with "Zipp" the grime solve will turn plastic/ paint to mush but will cause baked on fuel to literally disolve on contact and leave behind nice clean bright shiny metal, don't tell anybody I told ya it's a trade secret, it's extremely good stuff ya just gotta be careful what ya spray it on both products will haze plastic on contact and turn it into a gooey mess if you leave it there long enough