I tried a lot of things like paint stripper first, that worked pretty good. Then I finished with lacquer thinner (worked the best) and a few really cheap wire brushes from harbor freight. I have a thinner bottle that dispenses the thinner and just squirted it on the engine and scrubbed. I also found a very small wire wheel for a drill at Ace hardware that worked awesome for the corners and tight spots. I was surprised how clean I actually got the engine. I did break the spark plus off so I could get in there as well.