Ignition coil spark advance?

[dynodave]

What interests me is how the spark is generated, but also, as the OP asked, do these small engines have an advance
curve? There is a lot of hearsay out there, but little first-hand data that I have found. I have heard numerous times
that some of these small 2-strokes had "retarded ignition timing", which I doubted. My data shows, mostly as predicted,
that all of my sample engines have advanced timing, some with a continuous curve.

Without access inside one of these modules, we can't reverse-engineer the circuit, or place an oscilloscope probe
on anything but the HT lead. I am still in the process of non-destructive de-potting of a Husky 3-pole module, but
it has been slow. So far, I can see two separate coils wound around one pole, and a pair of poles. I soak it
in lacquer thinner overnight, which allows me to scrape off about a half mm of epoxy at a time.

I tried for years to find aftermarket substitutes for OEM igniters for one-cyl ATVs with dead ignitions. Of course,
these required a battery and a fairly hi voltage pulse off the engine's stator.

A magneto/flywheel driven EI/CDI is energy rectified and then power dumped to make spark is key concept in my book. I spent over 2 decade in electronics repair. You might find that rather than real "epoxy" these items are encapsulated in electronics "potting". They are quite readily depotted by scraping if heated with a heat gun to reduce its strength. I did tons of "depotting" including my dead 330 EI. I will admit to not being overly careful on that item and I might even continue from where the pix showed. I'm almost positive the coarse winding is the powering coil that is diode rectified into the big? cap...then the Capacitive Discharge Ignition is dumped/powered into the primary which will energize the fine wire high voltage secondary. Any advance (actually reduced delay) circuitry will likely be fairly simple. Sort of along the lines of a simple electronic tach circuit that alters the bias on the trigger of the (probably)SCR...based on RPM..

 

[X_makina]

You might find that rather than real "epoxy" these items are encapsulated in electronics "potting". They are quite readily depotted by scraping if heated with a heat gun to reduce its strength.

There are various types of potting compound out there for sure. It comes in different colors
and strengths, as does epoxy and polyurethane. A search on the web does not come up with
any single type that is most prevalent, other than "epoxy". Acetone attacks most of it, but dries
too fast and costs too much. Lacquer thinner is cheap, but does not attack it as well. I am
avoiding heat so I do not melt the plastics. I have not done very much depotting as it is a
PITA. I am sure you have done more than I have.

Inside this Husky module, I expect to find an SCR CDI switch like a TYN612, which are quite
cheap and common.

I remember a day when we modified our cars with CDI ignitions, back in the mid 70s. These
units were "dumb" in that advance was still handled by weights and a diaphragm in the disti.
By the early 80s, cars and m/cs had CDI, but conventional advance mechs. By the
mid 80s, you have smart CDI, with an advance curve handled within the igniter.

 

[X_makina]

I recently de-potted the Husky igniton module and here is what I found. This is a FOUR-pole
igniton, not a 3-pole as I stated earlier. My first impression is that I see why Husqvarna charges
so much for it....it is quite complex. There are 4 coils, and Coil #2 is comprised of 5 outer coils
and one inner coaxial coil. Coil #3 goes around 2 of the 4 poles.

Pole #4 is under plastic, and is quite small, with a tiny coil around it.

In the process of de-potting, the main capacitor, a film-type, fell off. There are also 2 PC
boards, with the main one having numerous SMD caps & resisitors, diodes, plus the SCR
and some unidentified devices.

This ignition module is unique to the 371K circular saw, AFAIK, and is different from that
of the 372, which shares most parts. The flywheel is also different from the 372. An
aftermarket coil seems to work fine in my 371K converted to chainsaw.

 

[MustangMike]

You are bringing back memories. I remember replacing the points on my Mustangs with Mallory Photo Cell Electronic Ignition, and then replacing the springs (with lighter springs) on the centrifugal advance weights to get faster timing advance ... the good old days!

When you had to know how to drive (no traction control), how to shift (a stick was faster than an auto) and how to work on your own car!

 

[X_makina]

You are bringing back memories. I remember replacing the points on my Mustangs with Mallory Photo Cell Electronic Ignition, and then replacing the springs (with lighter springs) on the centrifugal advance weights to get faster timing advance ... the good old days!

I am not so sure about "good old days". Doing tuneups all the time (filing points, setting dwell and ign timing, adjusting
carburetor) is gone. My engines now put out 2x the power/cc. My brother's 65 Mustang, which I worked on and
drove, often left me stranded.

Didn't Stihl have one of the earliest CDI ignitions back in 1968?

 

[MustangMike]

Didn't Stihl have one of the earliest CDI ignitions back in 1968?

Don't know.

Doing tuneups all the time (filing points, setting dwell and ign timing

That is why the Mallory Photo Cell was so nice, no more points + condenser. Improved reliability tremendously.

Yes the new motors are much more efficient, and I marvel at the power/gas mileage/ size of my current SC Stang.

On the flip side, I could do all my own work on the old motors.

 

[X_makina]

Personally, I love most of the new technology in modern cars: electronic FI, one coil per plug,
built-in diagnostics (OBD), reliable electronics, clean-burning, huge gains in efficiency, etc. I still do all my own work.

I do not like: push-button start, built-in navigation, heated/cooled/vibrating seats, needless repair-prone
complication. De gustibus non est disputandum.

 

[MustangMike]

Hey, to me the 2006 is a new Mustang, but I have a real ignition key that need to be inserted + turned, the lights do not come on unless you turn them on, and I can put my winter wheels on by myself because there is no TPM.

It was the 1st style V-8 Mustang to have multi valve heads (3 V) and VCT. They really make the Whipple SC come alive!

 

[LegDeLimber]

I recently de-potted the Husky igniton module and here is what I found. This is a FOUR-pole
igniton, not a 3-pole as I stated earlier. My first impression is that I see why Husqvarna charges
so much for it....it is quite complex.

X_makina, Did you use any sort of solvent to dissolve the potting compound or just pick it out like a Mad Dentist?
I would expect that at least a bit of aerosol can spritzing was used along the way.

 

[X_makina]

X_makina, Did you use any sort of solvent to dissolve the potting compound or just pick it out like a Mad Dentist?
I would expect that at least a bit of aerosol can spritzing was used along the way.

As I reported above, I soaked the module overnight in lacquer thinner, then scraped off a layer the next
day. I put the whole thing in a plastic bag to reduce evaporation. I did this more than a dozen times.

A heat gun would also soften the material, but I have not used that method much.

 

[LegDeLimber]

X_makina, Thanks.
Sorry for missing something that's still on the same page that is currently displayed. Trying to catch up on too many threads in a single sitting, I suppose.

 

[X_makina]

X_makina, Thanks.
Sorry for missing something that's still on the same page that is currently displayed. Trying to catch up on too many threads in a single sitting, I suppose.

No problem. I hope others report on what they have found inside these CDI modules. And how they
got in. The method I used only softens maybe a millimeter at a time.

The conclusion I can draw from this thread is that cheaper chainsaws have fixed, moderately advanced
timing, and expensive saws have an advance curve that advances more with higher RPM.