[The Newell]

If you have any build up, GUNK makes an engine grease remover. Just spray on, let set and spray it off. I have used it and it works good.
Usually they say to apply on a cold or SLIGHTLY warm engine-NOT HOT, including manifolds, so make sure you allow time for cooling before you start. Auto parts and most hardware's have it on hand. If you live in California make sure you get something biodegradable.