Small Engines (Lawn Mowers, etc.): snowblower, toro 421, spec number

Question
have a Toro 421 doesn't seem to want to stay running, tried feathering the choke, and no luck, not sure what goes bad on these, just got this one from a friend, and it ran good before i brought it home, carb has been serviced, so what else to check I'm not sure. Idle is at high right now, fuel issue?  maybe mixture of air/fuel is out. running super gas just in case. any suggestions, that i can check myself, before taking it in? Thanks

Answer
Hi Kirk,
How long will it run before it quits? It could be a tappet clearance issue. If it runs for at least 10-15 min. that's what it could be. If it's an adjustable carb, the bottom screw (high speed) should be set 1 1/2 turns open, the side screw (low speed) should be set 1 1/4 turns open. These may have to be tweaked while running. Also, give me the brand, model, and spec number of the engine. Let me know.
Thanks,
Keith