Small Engine Troubleshooting Problems? Ask a Mechanic Now.
If you're rewind starter works correctly when removed from the engine, then most likely your starter clutch is malfunctioning. Here's the replacement:
You can get it from any local Briggs dealer as well. Sometimes you can remove the screws and pop off the black cover and clean it without even needing to replace it.
This video will give you some additional information as well.
Hope this is helpful!