I have a JCB chainsaw and have experienced similar problems with the pull cord which seemed to slip when pulled. After stripping the cover of the pull cord housing I found that the Plastic lugs attached to the fan were partially siezed due to a build up of dirt and saw dust.These were cleaned with brake cleaner and lightly oiled on their pivots. Next the plastic drum that is located on the recoil unit was cleaned and all re assembled. This restored the chainsaw to full working order but I suspect that the process may have to be repeated occasionally.Total time spent was approximately 20 minutes.
Bob Hughes, November 2010