Hi there,

As mentioned above, its a good possibility that you've tipped the mower on its side. A 4 stoke engine like this has a wet sump of oil with an Air Filter on one side of the engine and an Exhaust on the other. It sounds very much like you have tipped the machine on to its Exhaust side and allowed engine to pass through the open Exhaust Valve and in to the Exhaust.

This would cause oil deposits on the piston / valves. However most of that is just down to age / use and happens to most engines after a while. The wet stuff is what has been forced through when the machine has been tipped over. As the exhaust box heats up it will burn off the oil and should clear on its own. Did you notice any oil coming from the spark plug hole when it was removed?

Again, as mented above, clean the air filter (if its the "sponge" variety or replace if its a paper cartridge type), replace the spark plug with a new one and while you have the head off its worth cleaning the worst of the wet gunk away prior to re-assembling the engine.

Re-fill the tank with fresh, clean fuel and check your oil level as this will have dropped due to the oil working its way through the engine. And away you go again...... in theory!

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