Stihl ms 661 cm mtronic has no spark!

[sawmill sam]

Hey all, I took my milling saws out of storage and a 661 won't start after 16 months on the shelf. Everything was fine when I put it away, This is the latest version m3 coil.
First I changed the plug, then I took the working coil from my other 661, still no spark. Checked ground and contact is good. What else is in the circuit? Could the fuel solenoid affect the spark?
I don't have a wiring diagram...thanks for any suggestions

 

[L34]

I know with a 441 if coil don't "see" the solenoid it won't spark.
Assume 661 is the same.

 

[sawmill sam]

So the next step is to swap solenoids I guess. I'll try it today. Thanks

 

[sawmill sam]

So the next step is to swap solenoids I guess. I'll try it today. So, if the solenoid dries out it can be problematic, similar to a carb. I won't be storing saws without fuel anymore! Thanks

 

[lone wolf]

The wiring harness should be checked with an Ohm Meter, and like mentioned the solenoid is suspect too. Did you try the basic kill switch disconnect ?

 

[sawmill sam]

The wiring harness should be checked with an Ohm Meter, and like mentioned the solenoid is suspect too. Did you try the basic kill switch disconnect ?

 

[Gord404]

I have a 661 here that does that, no spark when grounded to the cylimder but put it back in and it will fire up, sort of- runs like crap at this point, overly rich and won't idle at this point we are lookig for a non mtronic saw and switch it back to something more user friendly-today is 066 day- something that makes sense

 

[sawmill sam]

I have a 661 here that does that, no spark when grounded to the cylimder but put it back in and it will fire up, sort of- runs like crap at this point, overly rich and won't idle at this point we are lookig for a non mtronic saw and switch it back to something more user friendly-today is 066 day- something that makes sense

I actually have 3 661s I got in 2021 and they have been great until they got put away dry for 16 months. I suspect that whatever is wrong with mine, that is the cause. Milling is a retirement hobby for me so I will keep smiling . At nearly 72 years I feel lucky I am still able to wield a big saw. I also have 3 ms880's!
I upgraded from a reliable pair of 076's when I started out.

 

[SteveSr]

The M-Tronic saws have built-in diagnostics. If the saw fails diag then there is no spark.

Since solenoids rarely fail electrically my money is on a bad/intermittent connection in the wiring harness. Best bet is to remove every connector and shoot both ends with electronic contact cleaner (or non-chlorinated brake cleaner) and put everything back together. While you are doing this carefully inspect the wiring harness for pinches and other damage.

BTW, the spark may be hard to see in a lighted room. Best checked in the dark.

 

[sawmill sam]

The M-Tronic saws have built-in diagnostics. If the saw fails diag then there is no spark.

Since solenoids rarely fail electrically my money is on a bad/intermittent connection in the wiring harness. Best bet is to remove every connector and shoot both ends with electronic contact cleaner (or non-chlorinated brake cleaner) and put everything back together. While you are doing this carefully inspect the wiring harness for pinches and other damage.

BTW, the spark may be hard to see in a lighted room. Best checked in the dark.

Hi Steve, today I swapped carbs with my other 661 and it fired right up so the problem is not wiring it is part of the carb. Now I need to get a replacement solenoid I think. Can a solenoid dry up like a carb diaphragm? As I said, it sat for 16 months without fuel...
thanks for the reply

 

[Marley5]

Hi Steve, today I swapped carbs with my other 661 and it fired right up so the problem is not wiring it is part of the carb. Now I need to get a replacement solenoid I think. Can a solenoid dry up like a carb diaphragm? As I said, it sat for 16 months without fuel...
thanks for the reply

Sam, I may get flamed for this and that's ok, I have big boy feelings.
I'm 64 and was brought up and tought to leave gas in the tanks when stored, non ethanol of course.
I've had old homelites stored for years that I simply dumped the tanks and added fresh fuel and fired right up.

 

[Wood Doctor]

My favorite MS 661 C that I repaired. Great saw and still in use.
Here's what I had to replace:

 

[Gord404]

I'm 72 as well- today i finally got around to my keeper an 066 which is nice it has a decomp- going to keep this one, a friend gave it too me and once in a while I need something bigger than my 372

 

[SteveSr]

Hi Steve, today I swapped carbs with my other 661 and it fired right up so the problem is not wiring it is part of the carb. Now I need to get a replacement solenoid I think. Can a solenoid dry up like a carb diaphragm? As I said, it sat for 16 months without fuel...
thanks for the reply

Did you back substitute the "bad" carb to determine if it was really bad? Most likely there was an intermittent/bad connection at the carb solenoid which killed the spark. Fiddling with it fixed the connection issue. Hence my previous advice to clean/wiggle all the connections.

Solenoids usually fail from abrasives in the fuel and not electrically... which would kill spark.

 

[sawmill sam]

Hi Steve, today I swapped carbs with my other 661 and it fired right up so the problem is not wiring it is part of the carb. Now I need to get a replacement solenoid I think. Can a solenoid dry up like a carb diaphragm? As I said, it sat for 16 months without fuel...
thanks for the reply

Now I'm not sure about that black plastic piece with the wires attached to it that mounts over the solenoid. Do I replace that or the solenoid?

Did you back substitute the "bad" carb to determine if it was really bad? Most likely there was an intermittent/bad connection at the carb solenoid which killed the spark. Fiddling with it fixed the connection issue. Hence my previous advice to clean/wiggle all the connections.

Solenoids usually fail from abrasives in the fuel and not electrically... which would kill spark.

I thought I would put it back together tomorrow with the "bad" carb/solenoid and do as you suggest and clean the contacts. I'll report back. Thanks!!

 

[sawmill sam]

here's the culprit

 

[sawmill sam]

Sam, I may get flamed for this and that's ok, I have big boy feelings.
I'm 64 and was brought up and tought to leave gas in the tanks when stored, non ethanol of course.
I've had old homelites stored for years that I simply dumped the tanks and added fresh fuel and fired right up.

Absolutely! I shoulda known better! When I put everything in deep storage I got the dumb idea to drain 'em all and run 'em dry...And I've almost always used non-e fuel in all my saws and other 2 strokes

3 x ms880's
3 x ms661cm's
1 x ms660
2 x ms460's
1 x ms441
1 x 039
1 x ms310
1 x 025
1 x 024
1 x 021
1 x husky 61 300th anniversary edition
2 x 435's
3 x 2100cd's basket case saws projects
1 x basket case clone farmertec 880 project I got cheap to play with
1 x fs250 trimmer
and a couple other small project saws laying around

 

[sawmill sam]

I have a 661 here that does that, no spark when grounded to the cylimder but put it back in and it will fire up, sort of- runs like crap at this point, overly rich and won't idle at this point we are lookig for a non mtronic saw and switch it back to something more user friendly-today is 066 day- something that makes sense

I thought about switching to non-m also but it'll have to wait until the next time I have an mtronic failure (if it is a failure). I still need to clean the electrical contacts at the carb and put it back together and try once more. It could be just that and nothing else even though my saws are kept fairly clean. SteveSr and others have suggested cleaning contacts and checking the harness with an ohm meter

 

[sawmill sam]

Hi Steve, today I swapped carbs with my other 661 and it fired right up so the problem is not wiring it is part of the carb. Now I need to get a replacement solenoid I think. Can a solenoid dry up like a carb diaphragm? As I said, it sat for 16 months without fuel...
thanks for the reply

Now I'm not sure about that black plastic piece with the wires attached to it that mounts over the solenoid. Do I replace that or the solenoid?

Did you back substitute the "bad" carb to determine if it was really bad? Most likely there was an intermittent/bad connection at the carb solenoid which killed the spark. Fiddling with it fixed the connection issue. Hence my previous advice to clean/wiggle all the connections.

Solenoids usually fail from abrasives in the fuel and not electrically... which would kill spark.

I thought I would put it back together tomorrow with the "bad" carb/solenoid and do as you suggest and clean the contacts. I'll report back. Thanks!!

 

[SteveSr]

Now I'm not sure about that black plastic piece with the wires attached to it that mounts over the solenoid. Do I replace that or the solenoid?

I thought I would put it back together tomorrow with the "bad" carb/solenoid and do as you suggest and clean the contacts. I'll report back. Thanks!!

Any contacts that you touched, disconnected, or jiggled are suspect including the connector at the solenoid (that white thing on the carb).

Unless you are using canned gas (Motomix, Trufuel or equivalent) ALSWAYS drain and run dry. This is how saws come from the factory and can sit on the shelf for YEARS but always start right up. Even non-e pump gas looses the cooling volatiles over time as well as octane rating which the already lean M-tronic-strato saws don't like. Old gas is a good way to burn up a saw!

Don't confuse a fuel problem with a flaky electrical connection. Don't quote me but I think that the solenoids are like 35 ohms. Put your meter on the harness and start wiggling connections.