Most new engines now run a fixed jet carb, meaning that it is factory adjusted. When all conditions are met, clean air filter, proper fuel, clean and water free fuel, clean carb, will it run to their specs. The probem mostly cpmes from water in the fuel. Since the fuel now is blended with 10% ethenol alcohol, this is attracted like a magnet when condensation is present. This happens most from temp changes warm days/cool nights, and humidity. Water is heavier than gas, so it will form on bottom of fuel tank, carb bowl. or bottom of fuel can. It never goes away untill removed. If you were at the last of the fuel in your can, it is possible that water has passed into the mower fuel tank and if gravity fed to carb it went to the fuel bowl. Check all of these sources and let us know. Good luck:thumbsup: