What is a muffler safety shut off on a chain saw?

Remove the 2 screws "1" and "2" to remove the muffler.

Any chain saw store should be able to get what you need. Check what kind of saw you have, model number, etc. and then use the internet to find a way to order parts.

Sthil and Husqvarna are two different brands.

Husqvanrna saws are often refereed to as Huskys

Google Search "345 Husky muffler parts":
http://bit.ly/1igUxjF

Google Search "chainsaw parts / Stihl, Husqvarna":
http://bit.ly/1gSCye7

remove the muffler and try it carbon builds up inside and restricks the exhaust flow if runs with it off open the muffler and clean the screen inside

Their is a oil passage that has a plastic plug in it by the muffler. It might be gone like mine is.

There are a few things to check, if the muffler has a spark arrester gauze in the out let this may well be blocked, remove the muffler and the gauze, does the engine now rev? if yes either the park arrester is blocked or the muffler itself is blocked, if this does not cure it, check the flow of fuel from the tank to the new carb, replace the filter in the fuel tank and try again, if this does not help try running the saw with the air filter removed, if it revs normally the filter is blocked.

Too dangerous to describe over the internet. You need someone to demonstrate, or at least look at some pictures.

Try this one:
http://video.search.yahoo.com/video/play?p=chain%20saw%20safety&tnr=21&vid=544216450497&l=247&turl=http%3A%2F%2Fts2.mm.bing.net%2Fvideos%2Fthumbnail.aspx%3Fq%3D544216450497%26id%3D45e795adc8f834985077812a38f7b2e8%26bid%3D%252fkWIzMRyv1NECQ%26bn%3DThumb%26url%3Dhttp%253a%252f%252fwww.monkeysee.com%252fplay%252f16046-chain-saw-safety-considerations&rurl=http%3A%2F%2Fwww.monkeysee.com%2Fplay%2F16046-chain-saw-safety-considerations&sigr=123o1fbo7&newfp=1&***=Chain+Saw+Safety+Considerations

Just check that it has not picked up on the piston, remove the muffler and check the condition of the piston through the exhaust port, any sign of scuffing and the saw will need to come apart for further investigation.

There are a couple of reason the saw blade will not turn.
- Make sure you have bar and chain oil in saw.
-Make sure oil is running on the saw blade and chain.
-Make sure the clutch is not stuck.
- Make sure the bar sprocket is not frozen.
-The safety kick back guard needs to be re-set.
-Shut off saw. Push and pull guard.
Please let me know what you find.

carbs dirty need cleaning. try adding some stabil you can buy at auto zone with fresh fuel it may clean itself out w/o having to remove the carb.

If the muffler is clogged or damaged there will be too much back pressure for the engin to run. Check for free flow. Also, check the intake air filter to make sure it is clean so there is amaple air flow. Lastly, is there a safety shutoff related to the muffler that is being activated impropperly?