Hello Ellsperman,
Surging can be caused by one of two things: Either a dirty carburetor or the governor needs to be adjusted. You can clean the carburetor. Here's a link on how to do that:
Bitly.
If after you have cleaned the carburetor, the surging still persists, adjust the governor. Let us know how it works out!
When cleaning the carb, if you have to take it apart we recommend changing the gaskets because they may not seal the same again once they are opened up and this will cause a issue with how the engine runs. This would be the same for any gasket on the engine, if the part is opened we highly recommend the gaskets be changed out.