FONTE:
http://www.rc411.com/pages/howto.php?howto=29&page=5
a Pullstarts are common things in RC, especially in the RTR field. If ever your nitro vehicle needs to be started or restarted, all it takes is a few tugs and you're off and running. However, it's not uncommon to pull at the starter and all of a sudden find that it doesn't recoil. When this happens you're left scratching your head while a starter cord just dangles down from your chassis, swinging in the wind. Don't run to your local hobby shop to replace it, because it might just need to be rewound--saving you some cash and giving you peace of mind.
1. First things first--remove the engine from the chassis. This will give you access to the pullstart mounting screws and make the process much easier. In some cases you might have to remove the muffler/header assembly. If there's any oil residue, dirt, or gunk around the edge of the housing, clean that crap all off before you continue.
2.Identify the mounting screws for the pullstart housing. There are usually four screws around the edge of the housing; some use hex screws, some use Phillips or slotted screws. Choose the appropriate tool and carefully remove the screws, making sure you hold the pullstart housing against the engine backplate with your free hand.
3. With all mounting screws removed, slowly pry the pullstart housing away from the engine backplate. Inside, there will be a spool with the pullstart cord around it, a long, coiled metal spring (this might pop out of the housing if you're not careful!), and possibly the one-way bearing.
4. If it's a pullstart cord problem that's caused all the trouble, you'll have no trouble untangling the pull cord. If you happen to find a tangled and/or messy coil spring, you'll have to rewind and reset it in order to fix the issue.
5.Before you tackle the rewinding portion, take a moment and look at the coil spring ends. Generally one end will attach to the pullstart housing, and the other end will attach to the cord spool. Identify which goes where for reference. Also identify which way the coil spring should be wound; if the starter cord exits on the left, then the coil spring should be going outside-in, counter-clockwise (if you're looking at the inside of the housing). If the cord exits right, then it's the other way. Basically, the coil spring should be wound in the same direction as the starter cord.
6. Attach the spool end to the pullstart spool, then carefully wind the spring inside the spool cavity. Depending on the design, you may have to wind the spring from outside �in (like here) or vice versa. Every time you make one turn of the coil spring, put your finger on the spring to keep it from popping out.
7.When you're done, it should look like this. Note that the starter cord is still loose; without disturbing the coil spring you just spent a few minutes rewinding, reset the pullstart cord by winding it around the outside of the spool. Do this until the pullstart handle is tight against the housing.
8. Place the spool back into the pullstart housing, being careful not to accidentally unwind all the hard work you just finished. Here's where it gets a little difficult. Chances are that when you look inside the center of the spool, the end of the coil spring will not be in the right position to attach to the housing. This is because there is no tension on the coil spring. To get the coil spring lined up properly, you'll have to use some needle-nosed pliers or a thin hex wrench. Grab the end of the coil spring and wind it some more (while the spool is inside the housing) until the end of the coil spring will go back into its attachment position. Make sure to wind so that you're making the coil spring tighter, not looser!
9. It may take a little time, but eventually you'll get the coil spring attached. Once you do, go ahead and bolt the pullstart back onto the engine backplate. Make sure you orient the pullstart the same way it was when you removed it (match the shape of the housing to the backplate). With the pullstart housing back on the engine, give a few tugs on the starter cord. If all works well, you just repaired your pullstart!
TAP IT!
In some instances your pullstart cord might just be "stuck" and might not even have to be removed from the engine for repair. Sometimes the solution to fixing a loose pullstart cord is a few taps on the outside of the pullstart housing. All you have to do is take a small wrench and tap at the outside housing, and the cord will magically recoil back into the pullstart. This is a sign that there may be an accumulation of gunk, dirt, nitro oil, etc. that has collected inside the housing. The tap method will get you back on the track, but as soon as you get a chance, you might want to remove the pullstart and clean it out with motor spray to keep it smooth and trouble-free.
Conclusion
Repairing a pullstart is not as hard as it might sound. The key to a successful repair is identifying which direction the coil spring goes and determining how it attaches to the spool/pullstart housing. If you are able to identify those two things, then you can get your nitro back up and running in a matter of minutes!