Ignition timing

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Old2stroke

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With modern point-less ignition systems the basic timing is set by position of the coil and flywheel magnets relative to TDC of the piston. I believe the electronics in the coil module can as well effect the timing advance, does anyone know how many degrees of variability the module can achieve? I realize this will not be the same for all coils but what is your best info? 2 degrees, max of 5 degrees or more?
 
I have wondered the same thing. Especially about the newer “computerized” coil/control modules.

There is certainly a delay from the point the magnets pass the pickups to the instant of spark. I think most coils are designed as a more or less solid state which makes for a very short delay, nearly instantaneous. When you add a chip that can open or close a circuit, the range is probably limited by the chip and the ability to hold charge. I think the potential is there but it’s an additional complication. I don’t think it is typically done that way.

Also, I think the coil only has the potential to delay spark, not advance it. The magnets have to pass sooner or the charge isn’t generated.

Just my crude thoughts.
 
you can move a coil as far as you like surely ? (the spark will move accordingly, and affect the running of the engine) and the 2D advance map in the ignition module type is fixed i guess
 
you could check this... mark a EXACT TDC mark on the flywheel, yank the top cover off and run with just the starter unless you can figure a way to crank the saw up...
Whip out your timing light and connect it up, and let's see what the ignition is doing!

2 weeks ago I was working on a older 044, and replaced the seals, while I was putting it back together I discovered that the saw had a offset key. I had to think about it, and I put it back together so it was advanced slightly. THe saw ran nicely, so.... it probably would have the other way, or maybe with a straight key?

The M-tronic stuff is supposed to adjust ignition as well as fuel, I might be tempted to try a timing light experiment someday.
 
I set up an SP81E with a timing light to see what would happen as the RPM changes. My drill doesn't run up to 10,000 RPM so I could only see 3-5 degrees advance.

I know that on certain Stihl models (so I assume most others as well) the coil won't even generate a spark unless the engine I spinning over at least 600 RPM to avoid getting bitten by the starter handle.

DSC01967.JPG
The later one piece ignition coil gave a much stronger spark and more noticeable advance.

DSC01969.JPG

Mark
 
Some saws run around 28* of ignition advance and have zero curve, some models retard the timing at rpm increases, some advance as rpm increases. It’s completely model/coil specific

28* BTDC or 28* before spark?

How do they advance timing as RPM increases? Have a retarded timing at lower RPM?

Just trying to understand. I’ve always thought of the coil as one of the simplest parts of a saw.
 
28* BTDC or 28* before spark?

How do they advance timing as RPM increases? Have a retarded timing at lower RPM?

Just trying to understand. I’ve always thought of the coil as one of the simplest parts of a saw.
Most fire at idle at around 28* btdc. I have no idea about the inner workings of voodoo. Lol. But I’ve hooked a timing light up to several different models and paid attention to how much advance works well for each. Many of the newer saws, in my experience, have a built in retard at below idle speed to aid the ease of starting.
 
Most fire at idle at around 28* btdc. I have no idea about the inner workings of voodoo. Lol. But I’ve hooked a timing light up to several different models and paid attention to how much advance works well for each. Many of the newer saws, in my experience, have a built in retard at below idle speed to aid the ease of starting.

huskihl has it exactly correct. About the only thing to add is there is always two coils one for charging the circuit and one for the trigger.
They may or may not be noticeable. Especially on race motors I would set up a timing light and see if I was where I wanted to be. After several specific trials the flywheel would have several marks on it. Such as for low altitude runs I would retard timing as far as seemed reasonable. For high altitude advance as far as possible almost. Thanks
 
honda brought out an ignition module on their long running gx series, the magnet on the flywheel had a blue plastic collar and is positioned about 60deg advanced iirc ( coil and flywheel had to be run as a matched pair)
they were easier to start and drank a bit less fuel, and probably had a typical 4 stroke ignition curve
i think 2 stroke modules run a different curve that advances rapidly till 3k then falls away
 
Thanks guys. I am trying to mate a chainsaw coil with a lot of built in low speed retard onto a trimmer with a low fixed amount of advance. The result is the spark is so retarded it won't even fire so I am trying to get into the right ballpark of repositioning the flywheel for usable advance without too much trial and error.
 
Thanks guys. I am trying to mate a chainsaw coil with a lot of built in low speed retard onto a trimmer with a low fixed amount of advance. The result is the spark is so retarded it won't even fire so I am trying to get into the right ballpark of repositioning the flywheel for usable advance without too much trial and error.
To make it tougher yet, 2 similar sized coils from different make saws can fire 20-30* different from each other even though they’re mounted with the same 2 screws.

Just find a repeatable reference like tdc and mark the flywheel and cylinder. When you remove the fw, you now have a mark to refer to and can change the timing as required
 
Some comments and concepts.

The term "solid state" indicates that there are no vacuum tubes in the electronics. AFAIK not even old Russian saws had vacuum tubes in their ignitions. :D

Simple thyristor/FET ignitions come in two general categories. 2-legged and 3-legged. Both types have a voltage multiplier circuit to create a viable spark (some in unit and some in a separate module) and a primary coil that generates a pulse of electricity as it interacts with the magnetic fields of the flywheel magnets.
2-legged coils are able to vary ignition timing with RPM only by a very small amount, based on the small speed-related variations in the primary voltage.
3-legged coils are capable of wider timing variations because the 3rd leg, or pole, provides the circuitry with a varying interval analogous to the RPM.
Either type may also include a zener diode to kill spark below a certain RPM and/or a diode to prevent the engine firing in reverse.

Autotune/M-Tronic are a different thing altogether because the computer "reads" and "knows" the position of the flywheel thousands of times a second.
 
I found out the hard way that just because you can get a solid state module to fit and create a spark, the timing will not necessarily be correct.

i have an old Mcculloch Eager Beaver trimmer, the module was dead and NLA, anywhere. I bought a module that fit a different Mcculloch trimmer but looked almost identical. I was able to mount the module with very slight modification to where it mounted, set the gap and put it together. It has a beautiful hot spark, but I'll be damned if that MF timing isn't way off, it won't start but it pops like crazy out the intake and sometimes exhaust. I'd need to set up a timing gun to see how far off it is but for now F that trimmer, it's sitting in a corner...
 
On the 2100 husky I advance the timing the width of the slotted mark on the ignition body. I never went farther to see when it’s harder starting. Or ruining something. Good experiment to test it to advance it more. Not sure what rpms we can get out of it.

To advance with the ignition on the left side we turn the stator/ point plate clockwise. Just to make sure all of us are on the same page.

My big block Chevy I advanced the timing to 50 degrees at 2,000 rpm. Only me and another tuner know this when we talked. Gangbusters on the whole shot.
 
Husky I question that you moved your timing 50 degrees. I am not a big fan of Chevrolet but have worked and modified many of them, but nothing to do with 50 degrees. BTW Chevrolet is a great engine but just not for me because I understand Ford better. Thanks
 
Some comments and concepts.

The term "solid state" indicates that there are no vacuum tubes in the electronics. AFAIK not even old Russian saws had vacuum tubes in their ignitions. :D

Simple thyristor/FET ignitions come in two general categories. 2-legged and 3-legged. Both types have a voltage multiplier circuit to create a viable spark (some in unit and some in a separate module) and a primary coil that generates a pulse of electricity as it interacts with the magnetic fields of the flywheel magnets.
2-legged coils are able to vary ignition timing with RPM only by a very small amount, based on the small speed-related variations in the primary voltage.
3-legged coils are capable of wider timing variations because the 3rd leg, or pole, provides the circuitry with a varying interval analogous to the RPM.
Either type may also include a zener diode to kill spark below a certain RPM and/or a diode to prevent the engine firing in reverse.

Autotune/M-Tronic are a different thing altogether because the computer "reads" and "knows" the position of the flywheel thousands of times a second.

Very interesting. Is there an obvious way to identify 2-leg vs 3-leg? Can the 3rd leg be modified, or is the circuitry not obvious without a diagram?
 
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