The other night I picked up an old 1985 Johnson 9.9hp Seahorse for my boat the pull cord was badly frayed and not retracting. Back in the day this was a good outboard, so for $100 it was well worth the risk.
I suspected the recoil spring was either broken or badly corroded but before I could figure that out I needed to get the cover off, that actually took the longest amount of time to get working using penetrating oil, ball-pien hammer, and vice grip because the lever was broke off and badly corroded in the locked position.
Once I got the cover off I was able see pretty clearly that the recoil spring had slipped out of its housing. After removing the entire pull start mechanism I was able to clean a lot of gunk making the spring not work well, and reconnect it to the case it sits in. I picked up some poly cord, wound it onto the recoil spindle and.... it worked fine. After reinstalling it, I was able to start the motor with a couple pulls so I ran a bit of Seafoam mixed in with the gas and oil through it to start to get the carb clean after the motor sitting for some time. It seems to run well, at least without the load of pushing a boat.
I made a quick video of the old bird running, it actually runs well for what it is.