Broken/frozen throttle cable. Oil or replace.

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Missing/disconnected butterfly return spring on the carb. Hook up properly or get a new one. Stuck butterfly. WD40 until the butterfly works again. Grass, twigs, other debris jammed in the throttle linkages or springs. A good cleaning.

Basically, take off the air cleaner or whatever covers the carb area. Inspect it. Move the throttle cable and see if things on the carb move. Look inside the carb. There's a small circular plate with a couple of tiny holes in it blocking the throat of the carb. That's the butterfly and it's what controls the air/gas ratio and the speed. It should move freely but return to the blocked position by itself. If not, it's either gummed up and needs cleaning or the spring on the outside is disconnected or jammed. Another possibility is that the needle valve in the float is gummed up, but normally they gum up closed, not wide open. If all else fails then find someone with old lawnmowers in the front yard. He can fix it for $5. There are a lot of guys that tinker with small motors and they work cheap.