Small Engines (Lawn Mowers, etc.): How to get the string to go back in?, push mower, code numbers

Question
Hi

I am 12 years old and I have about a 7 foot gocart
I have a 3.5 push mower engine and
When I pull the string, it will not go back in and
there is also oil spitting on the sparkplug. I've already changed the oil.  

Answer
 Hello Jacob:

 Send me the Make, Model, Type and Code Numbers Off of the Engine, Please. They are Located on the Blower Housing(metal engine cover) just above the Spark Plug. With these Numbers I May be Able to Locate a Breakdown of the Engine and Better Assist you. The Spring in the Recoil is Most Likely Broken or Rust May be Preventing the Rope from Retracting into the Housing. Is the Engine Overfilled with Oil? Do you have the Correct Spark Plug Installed? Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John