Walk Behind Lawn Mowers

I purchased a walk-behind model 917.308451 last fall. I used it twice last year, then 3-4 times this spring and it started cutting out after 10-15 minutes of use. I brought it to a Husqvarna dealer and he said he adjusted the throttle governor, but it still failed after 20 minutes of use. Now it won't start at all.

Is this common? and is this covered under warrant? I bought it at Sears but don't want to keep pouring money into what was supposed to be a new, reliable lawn mower.

Thanks