kinda looks like water that has been in a really hot place with oil.
post a pic of your spark-plug end
if could be something else, but id start by checking the fuel system for water. Gasoline is lighter than water, so the water will be at the very bottom of the gas tank and may require some serious jostling to get it out. or empty tank and somehow use a fan and/or heat gun(hair dryer) to aid evaporation. you may also find water in the bottom of your float-bowl or even in the fuel filter. (edited)