Mower down

Hello,
My walking mower gasoline. We have made reparation before winter and have placed in the garage during the winter. I just go out and the have filled with gasoline. When I try to start by pulling on the thread, after numerous tests, it started but stopped after two minutes. In any case, on a surface without grass (terrace), it remains roughly on, but not on the grass (which is very annoying knowing it is there only to mow the grass).
It is all the time "teuf teuf" as on cars The air filter has to be normal.
So , I was wondering if anyone else had any idea? I thank you in any case and am sorry for the lack of technology!

Hi
Clean spark plug, drain the fuel tank and deliver fresh gasoline, check the oil ...

Otherwise he would have had to return to test repair, repairers have an obligation to achieve results.