I have a m2510, When pull the cord, it doesn't recoil or return, Tried several times to remove front housing, but I don't know how to remove the shaft or spacer and then access to the recoil starter.

Possibly the recoil starter pawl's on the inside of the recoil housing not engagning with the flywheel.

To replace the pull cord line:

If your pull cord is still attached to the grab handle, it's likely your spring is still wound. Follow this if this is the case, purchase rope of the correct length (or cut) and the correct diameter at your local lawn/garden store, then:
1. Disconnect the long drive shaft by removing the small set screw and the clamp - pull the shaft out of the engine body.
2. Remove the recoil assembly (About 5-5 torx bolts). You may need to disconnect a wire to the kill-switch at this time.
3. Pull the cord until it stops and use a small piece of wood acting as a wedge to jam between the recoil and the housing.
4. Cut the line and pull the knotted terminating end from the hosing.
5. Keep the wedge tight so it does not spin back. If this happens, you will simply need to rewind the spring back (about five turns) and re-wedge it.
6. Feed line through the recoil housing and into the recoil. Pass line through the hole in the recoil and knot the end. Trip to about .25 inch tail. Pull the rope through the grab handle and single or double knot this.
7. Remove the wedge and allow the spring to pull the rope back into the recoil.
8. If it does not completely recoil, either your rope is too long or you will need to add a "wind" to your spring buy removing the line and wind back 1 more turn. Retry.

Good luck!

Remove the tube that holds the flex drive from the end of the crankshaft. Lossen and remove the front cover. Remove the throttle cable from the carb. Remove the kill switch wire from the coil module. Remove clutch housing. Remove clutch, Remove flywheel. The recoil unit mates with the bottom of the flywheel and all the aforementioned parts are on the front side of the engine's crankshaft. Once you get the recoil unit off, you remove the old cord and turn the unit several times to "preload" tension on it. Insert the new cord into the guide holes and tie knots to lock it in place. The pull handle must be attatched too or when you let the recoil draw in the new rope, it will keep going and all tension will be lost. Reassemble all the above and good luck

Remove the tube that holds the flex drive from the end of the crankshaft. Lossen and remove the front cover. Remove the throttle cable from the carb. Remove the kill switch wire from the coil module. Remove clutch housing. Remove clutch, Remove flywheel. The recoil unit mates with the bottom of the flywheel and all the aforementioned parts are on the front side of the engine's crankshaft. Once you get the recoil unit off, you remove the old cord and turn the unit several times to "preload" tension on it. Insert the new cord into the guide holes and tie knots to lock it in place. The pull handle must be attatched too or when you let the recoil draw in the new rope, it will keep going and all tension will be lost. Reassemble all the above and good luck!
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Here is a condensed version of getting to the starter/recoil unit to inspect or repair.
Remove the tube that holds the flex drive from the end of the crankshaft. Lossen and remove the front cover. Remove the throttle cable from the carb. Remove the kill switch wire from the coil module. Remove clutch housing. Remove clutch, Remove flywheel. The recoil unit mates with the bottom of the flywheel and all the aforementioned parts are on the front side of the engine's crankshaft. Once you get the recoil unit off, you remove the old cord and turn the unit several times to "preload" tension on it. Insert the new cord into the guide holes and tie knots to lock it in place. The pull handle must be attatched too or when you let the recoil draw in the new rope, it will keep going and all tension will be lost. Reassemble all the above and good luck!

Remove the tube that holds the flex drive from the end of the crankshaft. Lossen and remove the front cover. Remove the throttle cable from the carb. Remove the kill switch wire from the coil module. Remove clutch housing. Remove clutch, Remove flywheel. The recoil unit mates with the bottom of the flywheel and all the aforementioned parts are on the front side of the engine's crankshaft. Once you get the recoil unit off, you remove the old cord and turn the unit several times to "preload" tension on it. Insert the new cord into the guide holes and tie knots to lock it in place. The pull handle must be attatched too or when you let the recoil draw in the new rope, it will keep going and all tension will be lost. Reassemble all the above and good luck!

remove the plastic housing to gain access to the recoil. Pull the cord slowly all the way out,this will cause the spring to wind up.Clamp the recoil wheel so it will not return to its original position,be carefull the recoil has tension on it not remove the old pull rope and thread the new one in and thru the hole of the recoil tie knot.pull on the cord to take tension off and at the same time remove clamp. Slowly allow the recoil to wind the rope in and reinstall on unit.

broken cord? remove bolts holding recoil housing.lift housing straight up,you may have to wiggle it a bit.turn housing over,remove any cord thats left,note how & where it connects to the spool.wind the spool [and consquently the spring under it]in the direction the cord would turn it as pulled when starting.hold spool tight.thread new cord through hole in housing.let spool turn back just enough to attach new cord.hold cord & housing,let spring "re-coil" cord slowly.check for smooth operation.replace housing.you may need to pull cord slightly to align 'square' shaft w/hole in spool.only after you are satisfied with the operation of it adjust length of cord by pushing excess cord through the handle,tie a new knot,then cut off excess,if any.

There is a spring inside the pull cord housing that makes the cord come back in, it probably undid itself, remove the housing cover and rope assembly and you will see the spring, you need to retighten it and place everything back. hope this helps