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#Post#: 87621--------------------------------------------------
Spark.
By: Jonjo Date: February 4, 2021, 8:48 am
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Hi,
Can anyone help me by explaining how stihl ignition module is
triggered? Is there more to the flywheel than the two obvious
magnets?
Any help much appreciated.
John.
#Post#: 87623--------------------------------------------------
Re: Spark.
By: 3000 FPS Date: February 4, 2021, 10:43 am
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Can you tell us what Model Stihl you are referring to. That
would help.
#Post#: 87624--------------------------------------------------
Re: Spark.
By: Jonjo Date: February 4, 2021, 12:29 pm
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Thanks for the reply. The thing I've got at the moment is a TS
400. It's actually a stone cutter but it's just like a
chainsaw. We've got about 10 chainsaws as well, various models.
What happened is that I rebuilt the engine but there wasn't
much of a spark when I'd finished. I bought a new module as
that has always worked in the past......but no joy.
Anyway I'm wondering if the flywheel could be to blame . I'm
basically very interested in how the spark is timed. I've
looked everywhere for info but as yet have had no luck.
John.
#Post#: 87625--------------------------------------------------
Re: Spark.
By: 3000 FPS Date: February 4, 2021, 6:32 pm
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As the magnets in the flywheel pass by the ignition module it
will build up a magnetic field and then collapse. When it does
it will induce a voltage in the coil of the ignition module and
will turn to a spark. It is a type of magneto. There are
other solid state devices in the ignition module like a steering
diode, capacitor, and I believe an SCR. I do not remember all
with out looking at a schematic.
The flywheel I believe is turning CCW so by moving the flywheel
from its keyed position CCW will advance the timing. Even
though this process starts before top dead center the actual
spark does not occur until after top dead center or else you
could have pre-ignition. Also the saw would be hard to turn
over and would kick back when pulling the rope.
The gap between flywheel and ignition module is critical and
most people here including myself use a business card for
setting up that gap. To wide of a gap could mean a weak spark.
The fly wheel should be keyed to a fixed position on the crank.
It could be possible if the magnet on the flywheel is weak it
would create a weak spark but I have never personally seen that
happen.
One other thing to check is compression. To low and it will
not start or run. Air, Fuel, Spark, and Compression.
One of the first things I always do to check a saw is to pour a
little fuel mix down the carburetor while holding the throttle
wide open. Pull it over and it should at least fire off a
couple of times. That will tell you it has good spark, good
compression, and that the fuel is going from the crankcase up to
the combustion chamber.
#Post#: 87626--------------------------------------------------
Re: Spark.
By: Jonjo Date: February 5, 2021, 10:45 am
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Thank you for your detailed reply. From what you say it's the
collapse of the field that determines the timing. The system
just seems a bit vague when compared with the opening of points.
Obviously the advance and rev limit are relatively
straightforward corresponding to rpm.
The magnets seem to have quite a reasonable grip on a
screwdriver. Somewhere I found a reference to a case where the
problem turned out to be a crack in one of the magnets. As far
as I can tell there isn't a cracked magnet.
I had my first Stihl in the early 60's and have had very few
problems over the years. I must admit that I just haven't got
the strength anymore to spin things over fast enough.
John.
#Post#: 87627--------------------------------------------------
Re: Spark.
By: 3000 FPS Date: February 5, 2021, 6:32 pm
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I looked at the parts diagram for the TS400 I do not believe
there are any points. It is all solid state in the ignition
module.
One other thing to look at. Set the gap for the spark plug at
.025 gap. Saws run better with that gap.
What I would do is to set the spark plug gap at .025 take it out
of the saw and hold it sideways on top of the cylinder with the
plug wire attached.
Then turn it over and see if you have spark. It will be easy
to turn over without compression and the plug will be grounded
to the cylinder so you do not have to worry about shock.
#Post#: 87633--------------------------------------------------
Re: Spark.
By: Al Smith Date: February 7, 2021, 5:20 am
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This is the best description of any I've found explaining how
the solid state ignitions work
HTML https://www.foxvalleykart.com/timing1.html
#Post#: 87634--------------------------------------------------
Re: Spark.
By: Al Smith Date: February 7, 2021, 5:22 am
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Part one of the above is points type and part 2 covers solid
state ignitions .
#Post#: 87641--------------------------------------------------
Re: Spark.
By: Jonjo Date: February 9, 2021, 3:14 am
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Thank you so much for the foxvalley link,very informative!
John.
#Post#: 87685--------------------------------------------------
Re: Spark.
By: Al Smith Date: February 18, 2021, 8:54 am
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I've got the theory of operation of the self advancing coils
used on the 042 and 048 Stihl models which is a little more
complicated .I may be mistaken but I think it works similar to a
Briggs and Stratton self advancing coil .Unfortunately I don't
think I can copy and submit that info .I'll delve into it though
.
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