Sorta a husqvarna guy...
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- May 30, 2016
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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 lessI 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.
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.
A mass air flow sensor would be incredibly easy to use on a saw as a simple tension wire under the intake .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.
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.