Lawn mower will run for 4 to 5 seconds and then quit....any ideas?

It's not getting enough gas for some reason. Could be sediment in the fuel tank covering the fuel outlet, could be a clogged or pinched fuel line, could be a gummed up carburetor. If it has a manual choke try closing the choke a little to see if it keeps running. You wouldn't want to run it this way, but that would tell for sure that it was starving for fuel. A clogged air cleaner would make it run slower, have less power, but it would probably still run longer than a few seconds.

Check and clean the air filter. Thats what mine needed earlyier this year. Also its good to have clean gas and new oil the in the beginning of the year and a new spark plug. But yours sounds like the air filter needs to be clean. Try pouring a little gas down the air filter hole and try and start it. It work on my rota teller

Check the air filter.