MS250

[ZeroJunk]

When the switch is in the off position it will be a dead short. Maybe .3 ohms on a good meter, which is mostly the resistance of the leads.

When the contacts are not touching you are reading the inductance through the ignition module which wanders around depending on the ignition, but it is lower on an ohm meter than one might think.

 

[Old2stroke]

Well, now that begs the question of how the OFF switch is actually working on an intact saw. If there is continuity whether the switch is open or closed, then how is that supposed to be working? Obviously I'm missing something here. Willing to hear more on this of course. Thank you for your input and interest in my thread.

If you have "continuity" from the ground wire at the kill switch, you are probably just measuring the resistance through the primary to ground which is very low. If you can read low enough values with your meter, it would show a low resistance NOT a dead short.

 

[ZeroJunk]

If you have "continuity" from the ground wire at the kill switch, you are probably just measuring the resistance through the primary to ground which is very low. If you can read low enough values with your meter, it would show a low resistance NOT a dead short.

With the kill switch in the off position it IS a dead short.

 

[ZeroJunk]

On a MS261 that I checked 5 minutes ago with a Fluke 87 III the off position is .3 ohms. A dead short for all practical purposes. The running position was 2.2 meg ohms . Will vary by coil I am sure, but it won't be zero. Although , 2.2 meg ohms is zero for all practical purposes in this application.

 

[Old2stroke]

With the kill switch in the off position it IS a dead short.

Yes of course, however the OP was questioning why he was getting a continuity reading from the coil kill wire at the switch with the switch open and my answer was the same as yours in post #21, probably reading the resistance of the coil primary. Without a schematic we don't know where the coil kill wire is connected but the logical place for most designs is where the electronic package is connected to the open end of the primary coil, as the other end of the primary and the free end of the secondary are connected together and to ground.

 

[ZeroJunk]

When he says continuity I would be curious what the value is and what he is testing it with.

I'm thinking if an ignition module reads completely open it's bad.

 

[stihltech]

OK time to grab your favorite beverage and sit for a minute.
Grab a know good plug, widen the gap WAY out, and check for spark. IF still none, check that the coil laminations are grounded to the cylinder through the wire from the coil to the cylinder.
Just remove the stop wire from the coil, or at least pull the wire out of the top shroud so you can see the whole wire and make sure it is not grounded anywhere.
No spark, now you have a bad coil.
As far as all this checking of coil resistances, most of us are not wasting our time with that, except for a good ground and no shorts on the switch wire. A snapped key will still give spark, but not start due to being out of time.
Maybe you have 2 bad coils, but chances are slim.
I look for a good used coil before I get an aftermarket one. Lots of them around.

Now finish the beverage, do the above, and let us know how you make out.
PS-there is a reason I mention the ground wire.

 

[ZeroJunk]

Here is something to put in the category of things you did not need to know.

Between the cutoff spade and ground on a MS261 the inductance measures 1341 milihenrys and the capacitance equals 8.295 microfarads .

 

[Old2stroke]

PS-there is a reason I mention the ground wire.

Go ahead we're listening. Are you referring to an older module where the coils are wound on a bobbin and the bobbin is pressed unto the core laminations with a coil ground wire brought out that is separate from the kill wire? The modern coils don't have a ground wire, the coils are mounted and potted directly on the steel core and their ground wire is welded to the core inside the potted assembly.

 

[stihltech]

It there not a wire that runs from the metal cylinder to the coil mounting screw?

 

[ZeroJunk]

It there not a wire that runs from the metal cylinder to the coil mounting screw?

I get them all mixed up, but there is one on the IPL.

 

[Old2stroke]

It there not a wire that runs from the metal cylinder to the coil mounting screw?

Is this just a wire that's added to ensure there is a good ground between the coil core and the cylinder?

 

[ZeroJunk]

Is this just a wire that's added to ensure there is a good ground between the coil core and the cylinder?

Yes.

 

[Opihi59]

When he says continuity I would be curious what the value is and what he is testing it with.

I'm thinking if an ignition module reads completely open it's bad.

I am a very unpretentious and unsophisticated person, I use an old Craftsman DVM that goes "beep" on continuity checks. Perhaps when I get back into this this weekend I'll post some lame photos. Honestly all I expect this saw to do is crank and run when it is needed.

 

[stihltech]

Well, without the wire you are relying on plastic to ground the coil. Last I knew, plastic is an insulator and a really bad conductor. The wire is not optional.

 

[ZeroJunk]

I messed around forever with an old Homelite and all I had to do was loosen and re tighten the screws holding the coil on.

 

[Old2stroke]

Well, without the wire you are relying on plastic to ground the coil. Last I knew, plastic is an insulator and a really bad conductor. The wire is not optional.

So this is a saw where the coil is mounted to the plastic engine case? I've seen the same thing with other saws where there is a built-in ground strap going from the coil mounts to the metal engine. Gotta love plastic, it's how we make them cheap and light.

 

[Gumneck]

Since no spark now, I'd be interested to the point of almost suspect that your original coil is ok. Hopefully you kept it just in case. I think it's time to start posting pics of the setup. One pic I saw in post 14 looked like a large gap b/n coil and flywheel. Could just be angle of pic though but looked more than a business card thickness to me.

 

[Patrick62]

Ok, I have been there and done that. yes the 250 will flood easy. Stihl Silver tech here.
Grab your compressed air hose. remove the plug, flip the saw upside down. blast air into the plug hole while pullin' the rope.
you can get the transfers, and the crankcase cleared out this way. Put a nice dry plug in there, NO CHOKE ! Fast idle isn't enough, Hold the trigger WFO, and pull the mutha'
It might pop. Pull the plug and repeat the air blast procedure
Try it again with dry plug. It will try and run.
Sometimes I would have to go a 3rd time to get one really flooded to fire up. Customer error....

We all know this, the starting procedure is to partially flood the engine, then high idle and she starts up.
If anybody (me included) pulls it one more time on choke... it won't start.

On a side note, check the gap on the coil to the flywheel. Also check if there is a square cast into the flywheel on the opposite side. One saw I fixed had the gap way out of specs. I adjusted it right, but would not clear that square... I filed that casting down, and the saw (a 250) ran very very nicely after that.