Stihl certainly has had issues with solenoid valves. Not all of them, but an unacceptably high percentage. The shop where I work sells $1M + in Stihl whole goods per year and I replace a solenoid valve every week or so. Not a bad average, but a higher incidence of failure than we should expect from Stihl.
The first generation MTronic fuel solenoids are prone to leakage. No whining, no excuses. This problem became apparent about a year into serious production of MTronic saws. For some reason, it seems to be almost exclusively on MS201's. The same solenoid valve was used on the larger saws too and I see very few of them fail, and I'll come back to this later. When the solenoid valve begins to leak, the saw's idle becomes erratic to non-existant, and the high end performance suffers.
I have a quick (not Stihl approved) test for possible solenoid valve failure: I start the saw with the throttle latched in the "triangle" position and run it at mid-throttle for about 10 seconds. I then idle it down and see if the idle is stable. If it falls on its face, runs rich. or dies, I move onto test #2. I then squeeze the trigger to full throttle and pull the rope. If the saw starts, it probably has a leaking solenoid valve. Remember, this is a strato-charged engine and they HATE to start at full throttle- it makes them go full lean by opening the throttle far enough to open the air-only strato side of the throttle valve.
If my quick test shows possible solenoid valve leakage, I then follow Stihl's solenoid valve test procedure to confirm my suspicion. Their test is 100% correct and accurate, but takes about 5 minutes to set up and perform. I can test a solenoid valve in about 20 seconds with my test and then decide if I move on to the "official" test. If you don't have SDS (Stihl Diagnostic Software) because you're not a dealer, you can't do the "official" test because you have to electronically operate the solenoid valve to pressure test it.
If I encounter a leaking valve, it gets replaced. No surprize there! There are 2 bits of good news about this: #1 is that the solenoid valve is a federally recognized emissions component and carries a 2 year parts and labor warranty. Even if Stihl's unit warranty has expired on the powerhead, the solenoid valve may still be covered. Once the solenoid valve has been replaced, I use SDS to reset the saw to its factory settings so it runs properly. If you don't have SDS, you can just go cut with the saw and it will readjust itself, it just takes longer for it to start running properly.
Stihl is aware of this issue, and any competent tech should be too. Stihl recently redesigned the solenoid valves and replaced the teflon valve disc with a stainless steel valve. The old style solenoid valves are black, the new ones are white. Unfortunately, they are not interchangable. You can't put the new style valve in an older saw. So far, I've only seen one leaking new style valve, and that was early into the production run. I am hopeful that this will be a lasting positive change.
One other issue is that I see patterns of valve failures in saws that are not well-maintained. Saws that have lots of debris in the fuel tank seem to often have leaking solenoid valves. We all have crap in our fuel tanks, but conscientious owners occasionally clean it out and replace the fuel filter. How much fine debris is getting past the fuel filter and causing premature failure of solenoid valves? Stihl has a new fuel filter #0000-350-3518 that is specifically for MTronic saws. Other than the orange-colored filter media, I don't know what the difference is. If I replace a solenoid valve, I clean the tank and replace the fuel filter. Perhaps a little routine maintenance will go a long way toward dependability.
Now, getting back to something I said early on. The solenoid valves are the same across the MTronic product line, but I see more failures in MS201's than all other saws combined. Is this because of the MS201's small displacement compared to other models? If a solenoid valve is leaking, it'll affect a lower displacement saw more than a higher displacement saw. Or, is it something else, such as a higher frequency of vibration from a high-revving saw damaging the valves? I don't really know. I suspect the larger saws aren't affected by a small solenoid valve leak AS MUCH as a lower displacement saw. I welcome you input on this one.
No matter what, MTronic or other electronic engine management systems are here for the foreseeable future until we get program fuel injection. I personally love the MTronic system- my MS261 freaking rocks! And it has been flawless for 5 years. I personally don't miss points and condenders, the Tyrannosaurus Rex, and lots of other old things. The new technology runs great. I, as an older guy, have to adapt and learn, or die off. I have made my choice, how about you?
