ArboristSite.com Sponsors


Stihl MS250 no spark

Honest John

Honest John

ArboristSite Operative
Joined
Aug 17, 2014
Messages
268
Age
42
Location
Klamath Falls, OR
I've been working on a MS250 today and I can't for the life of me figure out why its not getting spark. I started by switching out the ignition module from an 025 parts saw that I had. It looked different but fit just fine. When I switched them, I notice the pigtail coil inside the boot was a little loose so I pulled the boot off to re-seat the pigtail wire and then put the boot back on the 025 coil.

Still no spark....next step was to try a different plug. No luck there. After that, I switched out all the wiring from the 025 to the MS250....still no spark.

Any ideas on what I might be missing ?

John
 
Wood Doctor

Wood Doctor

Edwin
Joined
Jan 10, 2008
Messages
10,733
Location
Omaha, Nebraska
Grounded out or an open circuit? Seems like the switch could be bad. You might be dead before you try to start, regardless of your second paragraph above. Start checking continuity. You are not alone. Electrical problems drive everybody crazy.
 
Wood Doctor

Wood Doctor

Edwin
Joined
Jan 10, 2008
Messages
10,733
Location
Omaha, Nebraska
Go back to checking the spark. Make a spark checker wire. Use 12" of lamp cord, one side. Connect an alligator clip to one end, stripped 1/2" and strip 1.5" of insulation off the other end, leaving it bare. Clip the alligator to a cylinder fin. Remove the plug and wrap the 1.5" stripped end, bare copper, around the plug's threads and hold the wire firm to the plug. Dim the lights in the shop, turn on the ignition switch, and pull the starter cord a couple of times.

Did you see the plug throw a spark?
 
pantelis

pantelis

Addicted to ArboristSite
Joined
Oct 17, 2014
Messages
1,261
Age
45
Break in ignition lead or isulation damaged
faulty insulation or short-circuit in short circuit wire
ignition module faulty
 
drf255

drf255

BAD CAD
Joined
Nov 3, 2014
Messages
3,716
Age
52
Location
Socialists Republic of New York
Show a pic of your setup.

I've just done a bunch of 250's. There's a few different coils.

The coil should have 3 wires. One that plugs into the coil with a clip, one that has a round end terminal (both of these come from the wires in the handle/cover), and the jumper from the coil to the cylinder that grounds the coil itself.

The two wires come down through the cover, pass behind the spark plug wire in the plastic intake boot retainer. The green round end wire goes to the left, onto the engine bolt. In the same groove, the green jumper with the 2 round ends runs. It goes onto the engine bolt on one side and the coil bolt in the other. The black wire just clips to the coil.

Make sure that the clip wire and the round end wire do NOT have continuity. If they do, they're shorted and your coil won't make a spark.

Make sure that your switch is setup correctly. It's easy to have the flexible metal strip under the choke lever rod. It goes on top. One wire in the cover is connected to the strip, the other is the free end that slides into the choke rod. When the engine is turned off, these touch each other.

Gap your coil with a piece of paper folded over once. Put it over the flywheel, slipped coil towards it and let it stick to the magnets. Tighten top and then remove the paper. Check that it doesn't hit.

I'm gonna try to post a pic. I hope you get what I mean.
 
drf255

drf255

BAD CAD
Joined
Nov 3, 2014
Messages
3,716
Age
52
Location
Socialists Republic of New York
ImageUploadedByTapatalk1420881627.666341.jpg

Also, if you're coil is grounded (the body and not the clip) and you remove the clip and leave it bare, you should be getting spark if your gap is correct. It takes a fair amount of rpm to get a spark. You won't get one just turning the flywheel. You gotta put the starter on and pull fast.
Sent from my iPad using Tapatalk
 
Honest John

Honest John

ArboristSite Operative
Joined
Aug 17, 2014
Messages
268
Age
42
Location
Klamath Falls, OR
Yep, here's my setup with an 025 coil and wires. I can hold the plug in my hand and pull the starter and I feel nothing. I'm pretty sure I just happened upon two bad coils in a row. I ordered a new AM setup online and I'll switch out the whole thing when it arrives. image.jpg image.jpg
 
HarleyT

HarleyT

Tree Freak
Joined
Dec 6, 2014
Messages
16,396
Age
43
Unplug the wire/spade terminal going to the coil body, and leave it off... Now to properly test for spark, you need to plug the plug on the wire, and hold the metal side of the plug against the metal of the block somehow, not an easy task with these plastic clamshell models. I am guessing that you don't have 2 bad coils.....
 
HarleyT

HarleyT

Tree Freak
Joined
Dec 6, 2014
Messages
16,396
Age
43
I use a jumper wire with 2 alligator clips to ground out the plug, turn the lights off when cranking and looking for spark, and make sure that no excess fuel is in the cylinder or on the saw.
 
Honest John

Honest John

ArboristSite Operative
Joined
Aug 17, 2014
Messages
268
Age
42
Location
Klamath Falls, OR
I use a jumper wire with 2 alligator clips to ground out the plug, turn the lights off when cranking and looking for spark, and make sure that no excess fuel is in the cylinder or on the saw.
Yeah, tried with the jumper wire alligator clipped to cooling fin with the other end wrapped around the threads of the plug. Unplugged the black wire, and no spark.
 
HarleyT

HarleyT

Tree Freak
Joined
Dec 6, 2014
Messages
16,396
Age
43
From the looks of your crankcase housing, you have an old 025, the fuel caps tell me so. So you may need to step way back and look at the part number on the underside of that flywheel. If it is from one of the real old 025 ignitions, it may not be compatable....
 
HarleyT

HarleyT

Tree Freak
Joined
Dec 6, 2014
Messages
16,396
Age
43
Like in the 1980's, their switching over to electronic ignitions, well that depended on how many points/condensors that they had
on hand at the time......
 
drf255

drf255

BAD CAD
Joined
Nov 3, 2014
Messages
3,716
Age
52
Location
Socialists Republic of New York
Is it possible that your pigtail repair messed things up?

I'd put the old coil back on, gap it appropriately, keep the black wire off, and give it a pull.

Also, make sure that the green jumper from the jug screw to the coil is properly grounded to clean metal on both. Grounding issues can be a problem on theses plastic bodied saws. I'd sand the flat on the coil, the flat on the jug, and both round connectors with some fine paper.
 
Barge17

Barge17

New Member
Joined
Nov 29, 2019
Messages
1
Age
67
Location
Lancashire
Is it possible that your pigtail repair messed things up?

I'd put the old coil back on, gap it appropriately, keep the black wire off, and give it a pull.

Also, make sure that the green jumper from the jug screw to the coil is properly grounded to clean metal on both. Grounding issues can be a problem on theses plastic bodied saws. I'd sand the flat on the coil, the flat on the jug, and both round connectors with some fine paper.
I did the above yesterday with my o24 AV and it is now back to normal. Turning the lights off in the worshop as I tested the plug spark old me I was winning.

What a good forum I have found here, cheers
 
JLBMARTIN6

JLBMARTIN6

New Member
Joined
Mar 26, 2020
Messages
2
Age
56
Location
Ashland KY
I have a Stihl ms 250 no spark put new coil on gapped started right up turned off started ten times no problem it set for an hour now it won't start. took coil back off gapped again started right up then same thing tried new coil same thing again started right up fifteen times let it set for ten mins will not start any ideals
 
Top