Just cleaned a few engines tody using something I read about in an FM a few years ago. Dawn Power Disolver. Spray it on, let set 4 or 5 minutes, and brushed it off with an old toothbrush and soapy water. Cleaned off 20_ year old Castor based crud and dirt.
At work, we always filled the US cleaner with water, then put the items or circuit boards to be cleaned in a separate container with usually Isopropyl Alcohol. The cleaner's manual had several warnings against puting ANY flammable liquid direct into the tank. And for best results, the water level had to be at least up to the fill line, to make sure the liquid level was higher than the top of the Tranducer(s).
Caution...Power Dissolve will rust and corrode any iron,steel, parts or any other metal that will rust, it will also corrode your alum9num parts,
I have seen this several times with people that used Power Dissolve, SO make sure you completely take the engine apart, rinse every part well, and then make sure you oil the parts very well before putting the engine back together