2015 Ms181 Non Start - at my wits end!

[Darkslider]

Have done a search but can't find anything exactly relevant, trying to get the above saw going after it being progressively harder to start for a while now.

The saw has good compression: 150 psi after 2-3 pulls.
Carb mixture screws set to standard as per owner's manual.
Brand new correctly gapped NGK plug. 
New genuine fuel filter
new genuine air filter
magneto-flywheel gap checked and set (0.25mm/10thou)
fresh fuel that's reaching the cylinder (plug is wet after a few pulls)
when earthing the plug against the cylinder head I'm getting a spark. 

The only thing I'm not 100% confident of is the strength of the spark I'm getting, I'm used to a bright blue spark on vehicles but this is producing quite a weak yellow spark with both old and new plugs. I'm not sure if this is the norm for the little coil/plug setups on these saws or if this is potentially my problem, but I can't see what else it might be. I've read in my search so far that the coils are prone to failing regularly on the little Stihl saws, however at £50 for a new genuine coil I want to be 100% sure it's at fault before I spend ~30% of the saw's new price on one!

If there's anything I might have missed that could be worth checking out I'd appreciate some feedback.

Thanks in advance!
 

Edited June 25, 2019 by Darkslider

[Jwoodgardenmaintenance]

Order a non genuine coil and try that? 

 

Jack 

[AHPP]

Put MotoMix or Aspen in it. £20 and if it still doesn't work, you'll at least have some good fuel for its replacement.

[doobin]

1 hour ago, AHPP said:

Put MotoMix or Aspen in it. £20 and if it still doesn't work, you'll at least have some good fuel for its replacement.

What difference could that possibly make compared with fresh regular petrol? Save your money for the coil, which is the most likely culprit.

 

If it's not firing at all and the plug is wet, it's the ignition system. Can you borrow a coil to confirm?

Edited June 25, 2019 by doobin

[lurkalot]

Check it hasn't sheared the flywheel key, it has been known.

[Wedgebanger]

Putting in aspen or Moto crap in a saw that’s had petrol in it will require a carb rebuild. It’s well documented, you can’t do it....but the other way you can ie moto mix then petrol. But can’t go back to moto without a carb rebuild 

 

i would say yellow spark means either bad plug or coil.  More likely coil .

 

I would get get another know working plug and try that first.  And I said known working, it is unusual to get a duff new plug but it has been known..

one other thing, make sure that it is not flooded, ie switch it off and pull it over. Or leave it over night. Sometimes carbs go wrong and flood the engine, but as you say yellow spark I don’t think faulty carb.

 

When I have problems starting a saw , I try a squirt of carb cleaner/easy start/break cleaner  into the carb. It should fire on hot/fast start.

[spudulike]

Probably just needs a check over, OEM coils tend to be pretty reliable and usually either fail completely, have some weird sort of running pattern all the time such as not revving out or fail after a short running time and only work again after cooling.

 

Try bending the END metal electrode away from the middle centre electrode and if it will spark across around 5mm, the coil is probably OK. A bit cheaper than a new coil and AM ones are a bit hit and miss in the main!

 

Most issues are down to the carb so personally, I would get a new FULL kit in it and set it up/test it so I knew this was OK.

 

Aspen is no silver bullet, I have had a few customers ask if running on Aspen will sort out a running issue. If it runs crap on Petrol - it will run crap on Aspen. Aspen will clear out carbon on an old engine but is likely to cause carb issues and leaks down to the lack of petrol swelling the rubber but will be fine after an initial "changeover period" and replacement of rubber parts.

[peatff]

21 minutes ago, Wedgebanger said:

Putting in aspen or Moto crap in a saw that’s had petrol in it will require a carb rebuild. It’s well documented, you can’t do it....but the other way you can ie moto mix then petrol. But can’t go back to moto without a carb rebuild

 

A couple of my old saws are now run on Aspen and all I had to do to them was richen up the L screw a bit to get them to tick over. They have no problems running on it.

[spudulike]

The leaks and fuel line hardening usually happen after a few months to a year. A saw may run on it immediately but have seen a number of saws with annoying leaks when held vertical or on their sides. 

It will happen but is just the lack of petrol hardening the rubber - it won't happen on new rubber parts and only happens if the saw has been run on petrol for some time.

[bmp01]

Nice hot (way too hot to hold) spark plug will sometimes help if the fuel mixture is a bit off - you've just to figure out his to do it with the tools you have to hand ?

Been a few of these 171 / 181 / 211 won't start issues, and quite a few market carbs after which the requests for help dry up .... Trouble is without feedback we don't know if the repair worked or the saw was binned. 

 Where abouts are you ?