Chosen Solution
I have changed spark plug, then noticed that the air filter is soaked with gas
If it runs for a few seconds then quits, the float valve is sticking. The gas in the air filter means the needle valve is also sticking. Old gas has gummed up in the carburetor valves and needs to be removed. The carburetor needs a good cleaning. If you are good with this stuff, take the carb apart and clean it all out. If not, take it to a small engine repair and have them clean the carb. Should run fine when cleaned. Good luck.
