Completely disassemble your engine. Then gather some warm/hot soap water in your sink. Scrub each component lightly with your hands. Then leave the parts to soak in the water.

Take it out after 15-30 minutes. You can scrub with an old toothbrush if you want.

Also, some have been able to get their components sparkly by scrubbing it with toothpaste (no joke).

After all this, bathe the internals in some WD40 or nitro fuel or carb cleaner and blow em with an air compressor. If you don't have a compressor use an air can. If you don't have either, just blow and wipe. Then reassemble using a generous amount of after-run oil or some synthetic motor oil (Mobil 1).

You should have a new (looking) engine!