I'm just kind of curious if anyone knows the cause? I had the one on my Stihl MS361 fail last week Friday and I replaced it Monday along with a new spark plug since I couldn't remember the last time I changed it. I had noticed it was getting a lot harder to start, and then Friday even just a partial pull would cause it to pop without a sputter from the engine. With the new valve and spark plug in place, It's a heck of a lot easier to start and runs like a champ.
Most likely carbon buildup. My Mac SP125C starts much easier since I replaced the old points/condenser with electronic ignition module 2 years ago. Trying to start it without pushing that decompression button first will break the starter,your fingers or both..Havent checked in almost a year but compression after sitting a while was just under 200 PSI. However I have noticed that gradually over the past few months its starting to pop out pretty quickly also,barely half a pull & it'll snap your wrist. Until I get around to replacing that valve I just hold it in with 1 finger on left hand while pulling rope with my right. To do this successfully you have to kneel down,place left knee on air filter cover first so to hold the saw down,its not bad unless you have problems with hips or knees. And getting back up can be a challenge some days too That does the trick,unless I forget to do it like last Saturday morning.....
I recently plugged off my decomps on the 350 & 2166. Was suspicious of the valve on the 350 and I never use it on either saw. The 2166 is much easier to start under full compression and the 350 isn't bad at all to turn over. Best part is no more worries about leaks!
The original one on my stihl ms390 fell apart and dropped into cylinder and stopped the piston when it wedged between it and the head. No sign of issue at att till I was useing it and I heard a tapping I couldn't figure out. I reved it real quick to se if it went away. It got louder Then saw slowed and abruptly stopped. Looked like it only banged around in there a few times before it wedged. Least it didn't get hung in a part or something. I took the saw apart and pulled it out and replaced it and the saw still runs to this day. I was lucky.
My 361 would "pop" the decomp on every pull whether the engine fired or not. I took it out, soaked it with carb cleaner, gave it a once-over with a wire brush and blew it out with compressed air, and it worked fine after that.
My ms 460 ,and 661 do that . Gonna swap them out with decomps from husqvarna . Could be internet hearsay ,but I've read several times from pretty reputable sources that they are more reliable .
theyd better be for 30 friggin dollars. Ive also had success cleaning them, pretty simple technology.
Your dealer is abusing you if you're paying that . You can buy them all day long for < $14 (oem Husqvarna ) .
Nahh i havent bought one new, just looked online to see what they went for. My local dealer struggles to fulfill basic orders so i avoid him if possible. $15 is reasonable
I never have open one to see how is inside but when the decomp is new when it pop out it make a good " klic " noise and also is more dificult to press it in after of a long use the decomp start to be more soft and also i have notice that this " klic noise dont listen so strong so i believe that maybe the carbon maybe the heat destroy some kind of mechanism that the decomp have inside just my opinion
the sealing happens just by the tapered inside portion of the valve gets pushed away from the female surface, no different than a valve in a 4 stoke.
