Originally Posted by
Johnnojack
FWIW I have found the easiest way to remove stubborn carbon and greasy deposits is with a caustic cleaner, like oven cleaner, draino, or mild caustic soda (NaOH) and water, also some engine cleaners are slightly caustic and more gentle on aluminium. Liquid hydrocarbons like carb cleaner are fairly weak with carbon and only dissolve the grease. Use a nylon brush or toothbrush as caustic will eat up hair brushes and any other carbon based material (like skin) Wear specs and rubber gloves. Method just gently brush on solution, wait a while then rinse off with lots of water from hose. A plastic manifold could be soaked for a few hours then washed spotlessly clean with no damaging scraping or chipping needed.