Stihl MS-261C M-tronic with weak spark

[scottieamn]

I have read through the forums for answers and have tried a few solutions. No other threads have weak spark, they have no spark.

I have replaced the stock solenoid. Stock was black, replacement is white. The forums state the black was prone to failure and white is correct replacement.
I have replaced the ignition as well.
I had checked ignition gap before ignition swap and the new ignition is gapped correctly.

My next thought is flywheel has gone bad, not enough power produced.

I may need to swallow my pride and bring it in. I have never brought in a piece of equipment, but I have never had a piece of equipment with a computer/mtronic. So it might be time.

But first, what else should I try?

THANKS!

 

[ZeroJunk]

Some of the newer Mtronic saws don't show up on a spark test as blue hot like some older versions.

What was the original complaint ?

 

[singinwoodwackr]

I have read through the forums for answers and have tried a few solutions. No other threads have weak spark, they have no spark.

I have replaced the stock solenoid. Stock was black, replacement is white. The forums state the black was prone to failure and white is correct replacement.
I have replaced the ignition as well.
I had checked ignition gap before ignition swap and the new ignition is gapped correctly.

My next thought is flywheel has gone bad, not enough power produced.

I may need to swallow my pride and bring it in. I have never brought in a piece of equipment, but I have never had a piece of equipment with a computer/mtronic. So it might be time.

But first, what else should I try?

THANKS!

Check the plug cable. I’ve replaced 2 so far…usually corrosion.
cheap fix if the problem.

 

[scottieamn]

Some of the newer Mtronic saws don't show up on a spark test as blue hot like some older versions.

What was the original complaint ?

It was running great, then stalled. Fired up for 3 more seconds than never again.

I have tried with started fluid and still won't fire. Spark is really weak or non-existent.

Check the plug cable. I’ve replaced 2 so far…usually corrosion.
cheap fix if the problem.

There was a new cable with the new ignition.

 

[singinwoodwackr]

It was running great, then stalled. Fired up for 3 more seconds than never again.

I have tried with started fluid and still won't fire. Spark is really weak or non-existent.

There was a new cable with the new ignition.

Never use starter fluid on a saw! Good way to completely destroy the motor.

 

[singinwoodwackr]

do you have a multi meter? Start checking all connections for corrosion and loose fittings, and wires for continuity.

 

[ballisticdoughnut]

One thing to check is the spark plug itself. If it’s got the thread on tip make sure it’s tight. When they get loose the mtronic doesn’t like it.

 

[cscltd]

Compression?,
pull muffler and take pics

 

[Captain Bruce]

do you have a multi meter? Start checking all connections for corrosion and loose fittings, and wires for continuity.

Came here with a MS660CM a year or so ago. Giving me fits....There is an expert here. He jumped in and never left until I showed him the saw was back to work.

The M-tronic data was amazing. The culprit in my case, was a tiny yellow wire, that had pinched/rubbed thru. It showed up with a 10 buck VOM. Replaced the entire wiring harness. Saw went logging, and I went to bed.

Start with the simple stuff.........

 

[ZeroJunk]

I would really like to see somebody destroy a saw with starting fluid. That's funny.

 

[ZeroJunk]

It was running great, then stalled. Fired up for 3 more seconds than never again.

I have tried with started fluid and still won't fire. Spark is really weak or non-existent.

There was a new cable with the new ignition.

Look at the piston. If it is not scored that is number 1.
If you have changed the solenoid and the ignition that rules out most everything except the wiring harness.
Flywheel would be a stretch.
There have been reports of mismatches between module and solenoid where they would not talk to each other.
If it has compression and will not fire with mix poured in the barrel then it is possible the kill wire could have the ignition partially shorted off.

Like the gentleman above said, double check your compression. Check decompression valve.

 

[singinwoodwackr]

I would really like to see somebody destroy a saw with starting fluid. That's funny.

Into a 2 cycle cyl? Seems to have been covered here. Id never try it.

 

[huskihl]

Mtronic coils seem to like a slightly tighter air gap. And they need to be pulled over faster to show similar spark to older models. Make certain both ends of the coil wire are making good contact with their connectors and make certain there are no bare or pinched areas in the wiring harness

 

[stihltech]

What are you testing the spark with?

 

[oldbuzzard]

Ive bought and rebuilt many 261Cs.
Forget about the flywheel, they don’t go bad. It is either the module (coil), or simple wiring. You need a multimeter or simple continuity checker to make sure the wires are good and the kill switch hasn’t shorted out some how. On a 261C you also want to check the two wires that attached at the coil going to the carb to make sure they are tight.
You can go online and find a 261C Service Manual to get more details.
As one of the other members mentioned you need to make sure you are pulling hard and fast to get proper spark and it is hard to see. I test for spark in a dark garage.

 

[scottieamn]

do you have a multi meter? Start checking all connections for corrosion and loose fittings, and wires for continuity.

I have done a visual inspection and wires look new. I will check them individually. Sometimes it sparks weak. Sometimes not at all.

Compression?,
pull muffler and take pics

I'll probably check this last. The plug won't ignite gas dropped in cylinder with plug removed. I'm aware of the dangers of starting fluid and tried it to assure myself that it wasn't sparking. Do compression testers work on saws, I have 1. I also have a blowby tester, tests the rate compressed air leaks around rings at TDC. Pretty sure it isn't compression.

What are you testing the spark with?

Visual in dark, my finger on plug gap while grounded and pulling rope. Pulling with gas and then starter fluid in cylinder.


Thanks all for feedback so far. I wish I would have opened this topic a week ago when I last tried anything. I've been crazy busy since and am now out of town for another week. But I will definitely check in. I also bought a small ms170 that has been getting me by. But I've got a few downed big boys on my trails that aren't going anywhere until this is fixed.

 

[scottieamn]

I am hoping I can fix this without the shop.

I have:
5 atvs
2 jet skis
2 snowmobiles
Garden tractor
Walk behind mower
Rough cut mower
Backpack blower
Weed whip
Wood splitter
Post hole digger
Tiller
Power washer

Ranging from bought new, used, mechanic specials and many free on roadside.

Have never brought anything to a shop. Hoping to keep it that way. Yes, I'm stubborn, but also love tinkering with engines and doing engine maintenance.

Cars I bring into shop occasionally. Went last month for 1st time in 4 years because I had a vibration i couldn't find. I have 2 cars and a diesel. Wife and I both drive 20k a year.

Sorry if I'm bragging but I'm proud of my lineup and abilities. I'm the neighborhood go to guy for questions like mine. At work there is a 20 year old kid who knows more than me and can answer any car, truck/diesel or powersports question. Kid is amazing!

 

[lone wolf]

It was running great, then stalled. Fired up for 3 more seconds than never again.

I have tried with started fluid and still won't fire. Spark is really weak or non-existent.

There was a new cable with the new ignition.

OEM or China copy junk?
Did you disconnect the kill wire and look at the spark?
If so, it could be the flywheel.

 

[ZeroJunk]

Into a 2 cycle cyl? Seems to have been covered here. Id never try it.

I'm not trying to be argumentative. But, the starting fluid you get now is a far cry from the nearly pure ether you could buy in a can decades ago. You can actually get a saw flooded with it. And, it all has lubricants in it whatever the name is on the can.
I really can't tell any difference between starter fluid and just squirting mix in the barrel of the carb.
I keep starter fluid around because it is a good solvent and followed by compressed air gets something clean pretty quick and then it evaporates.

I certainly wouldn't squirt pure ether in anything, including tractors. Thought I blew one up about 50 years ago.

 

[scottieamn]

OEM or China copy junk?
Did you disconnect the kill wire and look at the spark?
If so, it could be the flywheel.

OEM. I don't think China has m tronic parts yet. I think they are to costly to copy to meet their margins.

Yes, I disconnected ground kill.