In the past, I've used Castrol Super Clean diluted 1:1 with water (to increase volume and reduce cost) in a steel wash tub and heated it over a camp stove. The parts were simmered for about an hour in this mixture. Other water based de-greasers may also work. All oil, sludge and grease were removed, as well as most of the carbon. The remaining carbon was very soft and easily brushed off with a brass brush. When clean, rinse the parts well with warm or hot water and dry thoroughly. Use compressed air if available, or a heat gun, or a cheap hair dryer (from a thrift store, not your bathroom!
). Then apply oil to prevent corrosion or rust. The parts will rust or corrode quckly as there is nothing protecting them.
Please wear long gloves and eye protection at a minimum!
A face shield and a respirator would be even better. Super Clean will remove all the oils from your skin and kill layers of it very quickly. Been there, done that, learn from my mistake! Cracking and peeling skin is painful.
I'd hate to think what it would do to eyes...