Small Engines (Lawn Mowers, etc.): craftsman 5HP 21 snowblower over revving, carburetor maintenance, carburetor overhaul

Question
Hello-- Problem of over revving sometimes. Cannot shut off with key  when this happens. Have to use full choke and push into snow. Thank you in advance for any suggestions

Answer
What is the model number?  Do you have a Tecumseh engine?  If so, check out this link:
http://www.cpdonline.com/692509.pdf

Also, search Google for Tecumseh carburetor maintenance or rebuilding.

Since you have to run with the choke on the carb is dirty.  Start with a carburetor overhaul and then we can tackle the over speeding if the carb job does not solve all your problems.
Let me know if this helps.
Eric