Air - fuel - ignition. Basics of all internal combustion engines. Have had many issues with lawnmowers over the years, but recently fuel is my most common one. Either wrong fuel, which causes fuel issues, or carb problems caused by the fuel. Replacement of the carburetor and use of alcohol free fuel has solved the issue over 90% of the time. No great mechanical skill required: empty fuel tank, removed fuel line, remove air filter, remove four screws, pop carburetor out of sleeve, slide off throttle lever. Assemble in reverse. And never reuse old fuel.