I HAVE A 310 STIHL CHAINSAW THAT KEEPS BRAKING THE JERK ROPE WHAT IS CAUSING THAT

SOURCE: 0340 AV stihl chainsaw won't fire

Spray a little starter fluid down the carburator . It is starts then is is a fuel problem. Most likely a gummed up carburator. Remove and clean . 

SOURCE: i keep breaking the plastic piece on stihl ms 250

before pulling descompress that little valve on the piston head

SOURCE: Stihl 015 Chainsaw - Change Pull Start rope

You have 3 screws to take out. 1 by the trigger and 2 on the side cover ( one on top and 1 on bottom).
The first thing you want to do is remove spark plug. After plug is removed carefully separate the housing paying attention not to lose the little spring holding the trigger when it comes apart. You can do this with the bar/chain on, but easier to handle without it. After it comes apart you can remove spring clip holding flywheel on. Be careful to lift the flywheel straight up slowly making sure the coil spring does not come up with the flywheel. If you just move it back and forth a little while moving the flywheel off the shaft. Take the rope off and measure it. I think its about 18" but try to measure the one on there. Make sure you knot the rope leaving a small tail so when the knot is tightened it has a little room to move without coming undone.After you wind the rope (clockwise) leave about 1/2 '' of rope sticking up in the notch on side of reel . Slide the wheel down and make sure the bottom notch on wheel is going to engage the coil spring when the wheel is turned.Replace spring clip on the shaft. If you have a problem with the clip, you may not be down far enough with the wheel. Turn the wheel about 1 1/2 to 2 full turns putting tension on the spring and making sure the rope sticking up is close to the the hole you need to string it through to tie in the handle. After you feed the rope through the hole (making sure you are adding more pressure on the spring as you pull the rope out, enough rope to work comfortably with the handle I take a fat bladed screwdriver and stick it down in between the wheel and housing to stop it from unwinding. Then string it through the handle with the same kind of knot used for the flywheel. After your handle is secure you can remove the screw driver and see how it works before re-assembling. Putting the housing back together requires patience making sure the housing fits over the flywheel and trigger area goes together nice.

Tips: If you need aid in stringing the rope through the handle I take about 6" of electrical tape wrap it around the end of the rope about 5 times and make sure as you wind the tape is moving towards the end of the rope and you can have a tail off the end of the rope to send through the handle. Good Luck
Rob

SOURCE: I need a service manual for a Stihl 310 chainsaw.

It can be downloaded here:
http://www.stihlusa.com/stihl_ownersmanuals/MS290_310_390_Manual.pdf
HTH
Lou

SOURCE: Im having problems starting an MS250 Stihl chainsaw. Can you give

Chances are good that the compression is not to blame. I would look at:
1. Bad Fuel
2. Fuel Line/filter
3. Carb dirty/mis adjusted
3. Spark Plug
4. Ignition