Idle / Throttle problem on my lawn mower?

When I start my mower it immediately rev's way up, then way down and it does this over and over until it finally just quits running. Ive replaced the air filter, spark plug and gas. Ive heard that it might be a carb or vacuum problem but I don't know what or where that is exactly. Anyone have some tips?

Answers:
Your carb is normally directly under or to the side of your air filter, depending on the brand. It's where the fuel and the air are mixed fro combustion. If you take the air filter off, you should be able to see a plate called the butterfly valve. When the mower is off, the plate should close the hole it sits in. Make sure the cable to the plate is also free from debris since this some times causes the plate to stick open and the idle flips around as the air/fuel ratio changes with each injection. As for a vacuum issue, hmmm, I'm not aware of a vacuum system on a mower! What brand is it?

Other answers:
What brand? Vertical shaft? Go over your carbs linkage.... sometimes the spring that holds onto the governor may wear out or break.
What brand? Vertical shaft? Go over your carbs linkage.... sometimes the spring that holds onto the governor may wear out or break.
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