Cook the engine or components (mufflers, headers, etc) overnight, on low heat, in an antifreeze-filled crockpot. No, I am not kidding.

Hot antifreeze works AMAZINGLY well. Best of all - no rubbing or scrubbing is required.

Required items:
- a 1 qt. (or larger) Crock-Pot
- a Gallon of Anti-Freeze (coolant for we southern types)

Warning: antifreeze is poisonous. Do not use the pot for cooking food after using it to clean engines! The vapours given off during this process probably aren't good for you either, so do this in a well-ventilated area. Finally, don't dispose the used antifreeze where your pets can get at it... dogs and cats like the taste of this stuff, and It Will Kill Them Dead.

Preparation:
Remove the muffler, glow plug and backplate. If your engine is completely gummed up with castor, you may have to remove the head as well. (Unless it's a Saito!) Place the engine and misc. components (not the glow plug) in the pot; pour in the antifreeze. Use enough to completely cover the engine.

Cover and plug in the Pot.

After 12+ hours, pull the engine from the pot. The hot antifreeze dissolves castor gum and varnish; carbon deposits are loosened and will generally rinse off with a quick spray of water. Furthermore, since antifreeze is formulated to work in your car's aluminum radiator, it does no harm to your aluminum engine.

Relube and assemble the motor, and you're done!