Chainsaw Repair

Sounds like it could be a tank vent or coil. After it dies, crack open slowly the gas cap close to your ear & see if you hear a suction sound.  If you do, that may be your problem, especially if it starts up just after that check.   I know you said you replaced the coil.  Sometimes you can get a bad replacement, even when new as I did on several occasions.  Aftermarket or otherwise. A bad coil can work fine until it gets warm.  Pull plug right after it dies, and check for spark.  If all checks out ok, you can move on.  Also, make sure there is a tight connection on that short impulse line from carb to bulkhead,  That's a common problem area on these saws.  May not be causing the problem you have now, but you do want it secure.  Good luck with it.  Those 51-55s are good ole saws.


Note:  Mr. Morgan has a good idea about the ignition switch.  Could be that as well.   They do go bad.