Video by Vespa Portland via YouTube
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Simple Green, soapy water, a brush, and a hose will get it done!
Leave the Simple Green and soapy water on for 5-10 minutes to let it work into the grime, then brush it down and spray it all off. This particular engine wasn’t in really bad shape but sometimes we get engines in here that look like the forest floor and this trick brings them right back to shining.