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Part Five: Ignition Timing

MustangMike

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I have never gone more than .030 off the key, as I would rather be safe than sorry.

I also believe that after that you get into diminishing returns.

I actually backed off a little on the timing advance on a ported saw that I had. I believed it got more torque after I did that.
 

smokey7

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Dont most cdi ignitions on a 2 stroke jet ski bike quad or sled advance up to a certain number then retard the ignition some after a certain rpm? I thought it allowed better high rpm with less advance at near peak rpm?
 

MustangMike

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I thought they just retarded the advance for startup, but I could be wrong.
 

Wonkydonkey

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Scott did a good vid on timing adv on the 462

this one sort of shows what happens. Although there’s probably more vids out there that explain and show it in more detail
 

ferris

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I think they can only retard the timing more or less. They became the signal from the magnetic poles on the flywheel. And the most important part, they became the energy for the spark from the poles. They can’t make a spark before that.
 

huskihl

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I think they can only retard the timing more or less. They became the signal from the magnetic poles on the flywheel. And the most important part, they became the energy for the spark from the poles. They can’t make a spark before that.
If the internal electronics are simple, then yes. Most coils that advance the timing with rpm have the flywheel clocked to the coil to fire earlier than what a dummy coil would be. They don’t advance the timing at higher rpm, they just retard it less
 

telejed

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Notice I said "as far as I know".

I enjoy these type of threads because we all get the opportunity to learn. When I did the first M-Tronic saws I did not advance the timing because I thought the system was controlling advance. Other guys reported that they were seeing good results with timing advance on these models......so, of course, I tried it. They responded just as well as any other Stihl did.

So, I've come to the conclusion (right or wrong) that the system cannot alter timing beyond the retard that is built in the coil for easy starting.

Without a mass air flow or manifold absolute pressure sensor, or an o2 sensor in the exhaust. . . I don't see much performance control for timing. All those things are what makes modern automobiles run as economically as they do. Oh, yeah. . . vacuum advance also not existing on saws.

Having a fairly shallow understanding of engines of any type, to get the performance like that requires some extra parts and more CPU than what is on any saw. Not saying it can't be done but, more to go wrong and a lot more weight. I was reading somewhere that vibration kills that kind of stuff.
 

Maintenance Chief

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Without a mass air flow or manifold absolute pressure sensor, or an o2 sensor in the exhaust. . . I don't see much performance control for timing. All those things are what makes modern automobiles run as economically as they do. Oh, yeah. . . vacuum advance also not existing on saws.

Having a fairly shallow understanding of engines of any type, to get the performance like that requires some extra parts and more CPU than what is on any saw. Not saying it can't be done but, more to go wrong and a lot more weight. I was reading somewhere that vibration kills that kind of stuff.
A mass air flow sensor would be incredibly easy to use on a saw as a simple tension wire under the intake .
The oxygen sensor would have to be a preheat and could be made much smaller for a single cylinder but oil mixes like to goo the muffler inside would probably ruin one pretty quick.
A centrifugal advance would work fine on a saw and the vacuum advances mostly went away for phase ignition Systems without vacuum signal.
If you weren't as concerned about emissions it would be incredibly easy to add multiple ignition timing features to anything but alot of the fuel efficient features wouldn't apply .
 

00wyk

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Chainsaws run at WOT/high RPM or idle most of the time. It's not too difficult to tune your saw at the factory for best performance with lowest quality available fuels for idle and typical WOT RPM ranges.
Though timing advances are important to performance with chainsaws, their largest benefit is throttle response and WOT. A chainsaw doesn't need to have as complicated a timing curve as a motorcycle or car, where the timing will change from idle to WOT and everything in between maybe hundreds of times during a commute or race, and where the engines mostly live nowhere near WOT. A chainsaw just needs to run well at WOT and idle.
 

MustangMike

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One of the most important reasons for a timing change on a chainsaw is to make it easier to start.

As you correctly state, almost all of its use will be at wide open throttle.
 

Lowey79

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Loving these “Theory” threads… Loads of great info!
Has anyone checked timing on a stock ms390? Are they fixed, or auto retard type coil? I know it’s a clammy, but it’s what I’ve got, and I love to tinker…
What’s a good target number as a starting point? 28-30° BTDC?
 

Mastermind

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Loving these “Theory” threads… Loads of great info!
Has anyone checked timing on a stock ms390? Are they fixed, or auto retard type coil? I know it’s a clammy, but it’s what I’ve got, and I love to tinker…
What’s a good target number as a starting point? 28-30° BTDC?

That saw has a 1300 "dummy coil". Likes some advance too. Just file the key till you can move the flywheel about 1/4" ccw at the outside edge.
 

mainer_in_ak

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That saw has a 1300 "dummy coil". Likes some advance too. Just file the key till you can move the flywheel about 1/4" ccw at the outside edge.

I've really enjoyed reviving one of these 290/310/390 series of saw. Was surprised to see the key was integral to the flywheel, but the ignition advance went OK.

I think it's the "free saw" part that makes them so much fun to work over.

The affordable aftermarket support was appreciated:

https://opeforum.com/threads/stihl-ms-310-rebuild.27032/#post-1386039
 

Stump Shot

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If anyone is still looking for a timing light that is accurate north of 10K, this is it….https://www.esitest.com/130.html It can be had cheaper from Amazon…

If you want advance features like rpm display and timing advance, this one from Bosch is excellent for 2-strokes.
While technically speaking it only displays to 9,999 rpm, it will go past no problem, just won't display the first 1 in 10,000.
So for example, 14,575 rpm would look like 4,575 on the digital display.
https://www.boschdiagnostics.com/products/digital-timing-light
OTC sells the same light... https://www.otctools.com/products/digital-timing-light-1
 
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