MS261C wont start

[Crispexx]

See that smushed yellow wire going from the coil ground ring terminal to the solenoid connector. That is NOT right and shouldn't be smushed. The saw and/or wiring has been incorrectly (re)assembled. This may or may not be your problem but deserves closer inspection.

Also, what is going on with the tape/sleeve on the red/black coming from the coil. Is that factory or an improvised repair? Looks like the wire color changes from red to orange?

Pull the remaining screw out of the coil and remove that connector. You should be able to measure the solenoid between the yellow ground ring terminal and the red/orange wire.

That tape is protecting the wires from their little spot on the body.

So here is the path of the wires. I’ve checked continuity and resistance between all the connections and as a wording harness fully connected and everything is good so far, last thing is the actual fuel solenoid


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[Crispexx]

Don't know if i mentioned earlier i do have access to an MDG and i can and have hooked the saw up to the SDS

 

[wyk]

Didja pull the top off the carb and checked it for blockage?

 

[Crispexx]

Didja pull the top off the carb and checked it for blockage?

I did, pulled the carb as far down as I could and it looked good, no chunks, debris or anything i could tell. Gave it all a good clean and out it back together.

 

[SteveSr]

That tape is protecting the wires from their little spot on the body.

So here is the path of the wires. I’ve checked continuity and resistance between all the connections and as a wording harness fully connected and everything is good so far, last thing is the actual fuel solenoid


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Now that the coil is loose and the end of the red wire is exposed try measuring the resistance of the solenoid (has to be plugged in) between the red wire on the coil and the yellow ring terminal. let me know the answer.

BTW, what kind of meter are your using?

 

[Crispexx]

Now that the coil is loose and the end of the red wire is exposed try measuring the resistance of the solenoid (has to be plugged in) between the red wire on the coil and the yellow ring terminal. let me know the answer.

BTW, what kind of meter are your using?

I’m using a Klein Tools MM300

And this is what I get

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[SteveSr]

I’m using a Klein Tools MM300

And this is what I get

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So the solenoid is about 36 ohms. Now pull thwe connector off of the solenoid and measure it there. Should be about the same.

 

[Crispexx]

So the solenoid is about 36 ohms. Now pull thwe connector off of the solenoid and measure it there. Should be about the same.

Nothing


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[Crispexx]

Nothing


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Realized I had it on the wrong setting, but I still got 0 Ohms


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[SteveSr]

Here is your likely problem... The yellow wire to the solenoid was smashed due to incorrect routing as shown in the photo below. It should run in the wire channel NEXT to the red wire from the coil. Yes, the channel with all of the sawdust in it! You might just try measuring that yellow wire while slightly bending or twisting it or you can also measure it through the solenoid. What you are looking for is the meter reading to start jumping around as the wire is moved. You can also look for any wire strands that may be exposed where the wire was smashed and/or may have shorted to the red wire or anywhere else.

 

[SteveSr]

Nothing


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No. Measure the solenoid resistance AT the solenoid (assuming that the test probes will fit and make contact).

 

[Crispexx]

No. Measure the solenoid resistance AT the solenoid (assuming that the test probes will fit and make contact).

Ok let me try this again...

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[Crispexx]

Ok let me try this again...

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I have a feeling you meant this


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[Overkill338]

IDK, but isn’t the new solenoid white and not black? I’ve heard the white is the universal upgrade and the black won’t always run right with the newer coils. Sounds like your saw is on the newer side.

The “brain“ of the MT is in the coil. I was told that the coil was lifetime guaranteed by Stihl to the original owner. I could be wrong there, but just going by what I have been told.

The MT carbs have only one jet and the solenoid controls the tune and rpm for choke/idle/WOT. It’s simplistic, but don’t I ever wanna fix them with a BFH when they act up and a screwdriver is useless.

Try different mix. I had one act up on me and that’s all it was. The mix was 32:1 Motul800 which is quite viscous. The time of year caused warm saw running conditions, but the fuel sat overnight and was chilled, adding to the viscosity. A swap to a 40:1 mix of a different oil and fuel solves my issue. This issue seems to be more prominent in the smaller saws like the 261. I’m assuming that the smaller tighter jet can have issues with flow secondary to viscosity.

Stihl set these saws up to run at 50:1 and actually tested them to 70:1. Adding more oil is just wasting money and spark plugs. I used to break them in at 40:1 until I took the Stihl unit I took on oil explained it all.

 

[stihl86]

You found a problem. Put the meter away and replace the harness. Without a constant reliable connection, the system breaks down and you're wasting your time. The connections get loose, also. Bar oil get everywhere, so a dirty connection is possible also.
Clean the contact points with cleaner and replace the harness.
Checking wires with a ohm meter is a waste of time in the real world.
The best way to check an circuit is with a voltage drop test. But it's not feasible in this case.
The SDS is close to useless for diagnosis. Its a 700.00 pos.
It is valuble for seeing hrs, to end the " I never used it" routine.
Also for recoving the fuel numbers.

The carb is very conventional.
Its still a 2 cycle. Use basic diagnostic procedures.

And calibrating is severely over hyped.
You cant change the preprogramed mapping
All you're doing is optimizing. And Stihl just loves that word.
The saw will relearn on its own after a few uses anyway.
It will not affect running behavior that much.

 

[Overkill338]

You found a problem. Put the meter away and replace the harness. Without a constant reliable connection, the system breaks down and you're wasting your time. The connections get loose, also. Bar oil get everywhere, so a dirty connection is possible also.
Clean the contact points with cleaner and replace the harness.
Checking wires with a ohm meter is a waste of time in the real world.
The best way to check an circuit is with a voltage drop test. But it's not feasible in this case.
The SDS is close to useless for diagnosis. Its a 700.00 pos.
It is valuble for seeing hrs, to end the " I never used it" routine.
Also for recoving the fuel numbers.

The carb is very conventional.
Its still a 2 cycle. Use basic diagnostic procedures.

And calibrating is severely over hyped.
You cant change the preprogramed mapping
All you're doing is optimizing. And Stihl just loves that word.
The saw will relearn on its own after a few uses anyway.
It will not affect running behavior that much.

You use Stihl's special wire tucking tool, with press fluid.

 

[SteveSr]

The method of tracing down intermittent open circuits is to get the circuit into the failed state, like it was, and then verify it WITHOUT disturbing it. Yes, this may take some finesse and practice. The solenoid is connected between the coil/saw ground and the red coil wire. These are your access points for if/when this reoccurs.

If it misbehaves again connect the meter across the solenoid at the ignition module and then very gingerly start poking/prodding the wires and connectors between the coil and the solenoid until the connection makes again. The most sensitive spot is likely your bad connection.

Unfortunately, disturbing the harness and moving everything around likely caused the issue to go away as moving metal against metal will scrape the insulating oxide away and make the circuit complete again until the oxide builds back up.

I would probably trade out the section of the harness with the smashed wire, install the new one correctly, and then put it all back together. I suspect that it will run fine. Hopefully the problem has gone for good.

 

[SteveSr]

The SDS is close to useless for diagnosis. Its a 700.00 pos.
It is valuable for seeing hrs, to end the " I never used it" routine.
Also for recovering the fuel numbers.

So will the MDG not diagnose solenoid and harness failures like opens and shorts?

 

[stihl86]

You use Stihl's special wire tucking tool, with press fluid.
View attachment 839864View attachment 839865

I use the tool all the time at work. I tried the fluid and it’s a little to expensive for me. A weak Dawn solution

 

[stihl86]

So will the MDG not diagnose solenoid and harness failures like opens and shorts?

As with any diagnostic program, it’s far from 100%. If a wire in the harness is broken, yes it will.
Very rarely are things cut and dry.You know that. If the solenoid has failed completely, yes.
Wont tell you if it leaking. For what it costs, along with the constant updates, in our shop, it’s rarely
used. It’s caused me to chase my tail penty of times. Now, with a no spark, or more often, spark once, the harness gets replaced. Cheap enough and easy to do. No idle, replace solenoid.
But only after I go through the usual troubleshooting procedures.
Everyone always goes to the electronics and disregards the wiped out piston because the compression was “good”

We’ve had the SDS since it came out. $695.00.