I'm a master hvac tech and use some stuff called grimesolve this stuffis designed specificly and very effectivelyto remove baked on fuel residueand will take baked on fuel oil off porcelin electrodes on contact I tried it on my stuff and it works instantly, but and theres always a but, do not use it anywhere near plastic orrubberit is a chlorinated solvent andwill turn those 2 things into asticky swelled up mush