So I bought this mower new about 2 years ago. Right out of the box the mower contentiously sounds like it revs up and down, hunts and surges I guess. I should have taken it back to home depot to have them fix it but I never did. It cuts fine, doesnt die, its just really annoying that its not running properly. I have cleaned the air filter but that did nothing. Could it be a carb screw, spring, etc? Thanks!