Stihl ms261 piston question (burned)

[Crispexx]

MS261C wont start

MS261C wont start

Afternoon all, Might as well start off saying I'm not a Stihl tech and far from one, but I pick things up fairly quickly. I work for a fire department in California and we have A LOT of saws and a few of us are fairly saw savvy despite our lack of professional training. I have access to an SDS...

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This is a thread from last summer when I was working on a 261c that wouldn’t run properly. I ended up getting ahold of a friends 261c and swapping the app ignition module and it fired right up.


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[SteveSr]

I also removed kill switch + red wire that leads to carburator - no spark

@SteveSr - You mentioned continuity on the carb wire, can you perhaps explain a way to test this?
I tried to touch the "red wire" end and other end to metal - it showed it had continuity. But can I even test it like that?

The wiring harness must be complete, intact and completely connected for the M-tronic system to work and produce spark. Randomly disconnecting chit and expecting results is going to result in nothing but more frustration. This is definitely NOT your standard ignition system.

Wiring harnesses are also known to fail and become intermittent. This may be why the saw is all gunked up. The system defaults to "rich" to keep from burning up the engine. You likely have a carb solenoid / wiring harness problem. A wiring harness is cheap, especially compared to a coil.

If you have the older black carb solenoid you need to replace it with the newer white version and also change to the new orange fuel filter/pickup.

There are plenty of threads on troubleshooting M-tronic systems on this and the "other" site.

 

[MartDalb]

The wiring harness must be complete, intact and completely connected for the M-tronic system to work and produce spark. Randomly disconnecting chit and expecting results is going to result in nothing but more frustration. This is definitely NOT your standard ignition system.

Wiring harnesses are also known to fail and become intermittent. This may be why the saw is all gunked up. The system defaults to "rich" to keep from burning up the engine. You likely have a carb solenoid / wiring harness problem. A wiring harness is cheap, especially compared to a coil.

If you have the older black carb solenoid you need to replace it with the newer white version and also change to the new orange fuel filter/pickup.

There are plenty of threads on troubleshooting M-tronic systems on this and the "other" site.

So, the smart tech of the machine can actually prevent the coil from making a spark?
If say there is a faulty wire to the carb or a stuck solonoid etc?

Man....I always felt like the more tech takes over, the harder it becomes for DIYs to keep up....
That's why my car is old and will never, hopefully, be replaced

Anyhow, I will be taking a look at the wires and solonoid now.
Meanwhile, I put some stihl folks at work looking for a used, working, coil!

 

[MartDalb]

Meh, cant take a look at the solonoid.
This little torx10 has a little needle in the middle. Don't have that sorta tool.

That's no good. Ill get a tool for that

 

[Crispexx]

Meh, cant take a look at the solonoid.
This little torx10 has a little needle in the middle. Don't have that sorta tool.

Well at least you know it’s the updated black solenoid.


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[SteveSr]

So, the smart tech of the machine can actually prevent the coil from making a spark?
If say there is a faulty wire to the carb or a stuck solonoid etc?

Absolutely! It can't verify the operation of the solenoid until it runs but it can check for obvious issues like open circuit before allowing it to run. An open solenoid or wiring fault would allow excessively rich operation which the emissions authorities wouldn't allow. This is the same reason saws will NOT run on full choke.

Anyhow, I will be taking a look at the wires and solonoid now.
Meanwhile, I put some stihl folks at work looking for a used, working, coil!

You should probably also hit the connectors (both pieces) with either contact or non-chlorinated brake cleaner to ensure good connections.

When working on M-tronic systems parts should be verified/replaced in this order.
1. Wiring harness.
2. Carb solenoid.
3. Ignition module.

 

[SteveSr]

Meh, cant take a look at the solonoid.
This little torx10 has a little needle in the middle. Don't have that sorta tool.

That's no good. Ill get a tool for that

Those are called tamper-proof Torx fasteners and tools are readily available.

 

[MartDalb]

Well at least you know it’s the updated black solenoid.


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Wasn't it the "white" that was updated?

 

[SteveSr]

Well at least you know it’s the updated black solenoid.


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Is black the new one? I thought that it was white.

In any case Stihl learned that the original non-orange fuel pickups would let fines through that would eventually damage the solenoid in the carb. They made some improvements to the solenoid and also released an improved "orange" fuel filter.

 

[MartDalb]

Absolutely! It can't verify the operation of the solenoid until it runs but it can check for obvious issues like open circuit before allowing it to run. An open solenoid or wiring fault would allow excessively rich operation which the emissions authorities wouldn't allow. This is the same reason saws will NOT run on full choke.


You should probably also hit the connectors (both pieces) with either contact or non-chlorinated brake cleaner to ensure good connections.

When working on M-tronic systems parts should be verified/replaced in this order.
1. Wiring harness.
2. Carb solenoid.
3. Ignition module.

Noted, and I will redo my inspection. And check out that solonoid, once a T10 with a hole arrives to me.

This saw, is just really not that used, it's not dirty, or smeared at all.
It was on the "outside" but the wires, contacts are crystal clear and seems brand new?

 

[MartDalb]

Is black the new one? I thought that it was white.

In any case Stihl learned that the original non-orange fuel pickups would let fines through that would eventually damage the solenoid in the carb. They made some improvements to the solenoid and also released an improved "orange" fuel filter.

This could explain why the carb, was so nasty inside? Check the pictures I put up.

 

[SteveSr]

This could explain why the carb, was so nasty inside? Check the pictures I put up.

I remember those! It was run without a fuel filter at all. Plan on replacing the solenoid. I am sure that the one on there is trashed. Also make sure that the fuel hose is not cracked which would cause the same issue.

 

[Crispexx]

Is black the new one? I thought that it was white.

In any case Stihl learned that the original non-orange fuel pickups would let fines through that would eventually damage the solenoid in the carb. They made some improvements to the solenoid and also released an improved "orange" fuel filter.

Yea y’all caught me, I miss typed. Black is bad. And yes the orange fuel filter is also an update.


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[MartDalb]

Yea y’all caught me, I miss typed. Black is bad. And yes the orange fuel filter is also an update.


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Would have rather had it the other way around!

 

[Crispexx]

Would have rather had it the other way around!

Even if the black solenoid was the updated one it’s still probably toast since you found the carb looking like that

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[MartDalb]

I remember those! It was run without a fuel filter at all. Plan on replacing the solenoid. I am sure that the one on there is trashed. Also make sure that the fuel hose is not cracked which would cause the same issue.

This "cheap" saw turning out to be way too expensive for my liking!

If it's a new coil + solonoid, would be like 4 times what I paid for it.

 

[MartDalb]

Even if the black solenoid was the updated one it’s still probably toast since you found the carb looking like that

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Ok, I haven't seen these micro solonoids, but I will add.
Solonoids on my lawn tractors are fixable, atleast for a time, not the case for these I guess?

 

[Crispexx]

This "cheap" saw turning out to be way too expensive for my liking!

If it's a new coil + solonoid, would be like 4 times what I paid for it.

I would wait on that coil, those normally are pretty solid. Like stated above look at that solenoid and wiring harness for possible faults first. What did you get this ‘cheapish’ saw for?


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[MartDalb]

And...this shiz is starting to bother me, I have seen 026s 025s 023, etc etc. with 20+ years on them, burried in dirt, and they would still run, after a good carb clean or similar.
This damn saw is looking brand new compared.

 

[Crispexx]

Do you have the IPL and service manual for this saw? I can send you what I have if needed. Part number 1140 007 1802 is the updated fuel filter and solenoid for this saw.


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