hey buddy how's it going??
I just signed in (this is my first post!) so hey to everyone else in the forums.
Regarding your problem, it sounds like your one-way bearing is slipping. This would cause the cord to not wind back in. Try cleaning the one-way bearing, as oil can get on it and cause it to slip.
The spring in the pullstarter has to clip inside that little 'c' shape molded into the pullstart case. I have the HPI/Novarossi Evo 2 pullstart engine and just yesterday my spring snapped inside the starter. I bended it to the shape it was meant to and clipped it inside the c shape, making sure it didn't pop out, and now it works fine.
Hope this helps, if you have any other problems let me know