hi my ms391 blew the decompsession valve clean off . i had used it to make two cuts . literally 3 min warm up 3min work. gave it a min at idle and was about to trigger it off when it just quit . took me a min to figure out WTH had happened and never did find the valve. ordered a new one did a little research that gave me no insight as to what the issue may have been. no damage to the spark plug , it was brand new still looks new. piston still moves i did not put a gauge on it yet but it is getting compression and spark. after new valve it of course does not start. what i could see of the cylinder wall appears worn but nothing obvious jumped out at me. i know enough to make some educated guesses and am old enough that i was taught the lost art of critical thinking but my experience is mostly older vehicles not so much small engines and i know that saws are not weed eaters. some advice from those more experienced than myself as to an avenue to pursue would be greatly appreciated.
decompression valve on ms 391
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Gosh, that seems unusual.
How do the valve-threads in the cylinder look? If they are OK, my guess would be defective threads on the valve, or valve-not-torqued-down.
With the latter being the most likely.
Would have been good to have been able to find the valve.
Roy
How do the valve-threads in the cylinder look? If they are OK, my guess would be defective threads on the valve, or valve-not-torqued-down.
With the latter being the most likely.
Would have been good to have been able to find the valve.
Roy
If you are a torque-wrench-kind-of-guy, the shop manual will have a spec for that valve. You can get the manual using the Beg For Manuals thread on this site.
Roy
Roy
