Author Topic: Chainsaw ignition timing  (Read 201 times)

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Re: Chainsaw ignition timing
« Reply #10 on: October 17, 2016, 12:18:23 am »
If you think then that the timing is retarded that bad then pull the flywheel and advance it to where you think it should be.   You do not need a key in the flywheel if the nut is tight on the flywheel.  Prove to yourself if it is correct or not.    Just move the flywheel in a CCW direction to advance it.
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Offline Al Smith

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Re: Chainsaw ignition timing
« Reply #11 on: October 17, 2016, 05:28:44 am »
Some solid state coils have a built in advance which works by detecting voltage which is dependent of rotational speed .The faster the rotation the higher the voltage until coil saturation won't increase the voltage.

Two examples of failures I've encountered on this design .Briggs 18 HP twin.It would fail on full advance and fire so early you could not get it started until it cooled off .042 Stihl that would not advance,I doubt it would turn much over 6000 RPM under this condition .

I'm not familiar with the coil in question weather it's an advancing type or not .Usually that kind either has three coil stater  pieces or three magnets on the flywheel or at least the ones I've seen do .What you have I don't have the foggiest idea .--more --

Offline Al Smith

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Re: Chainsaw ignition timing
« Reply #12 on: October 17, 2016, 05:38:29 am »
--now then .Coil voltage is dependent on three things,rotational speed,lines of magnet flux cut and air gap of the coil to fly wheel ,faster means more,closer means more ,position the coil fires at in relationship to the magnets.

If the coil fires on the leading or trail edge of the magnets the voltage will be less,dead center magnetically will be the highest .

The reason you need advance is to "light the fire" so the max rate of expansion occurs at slightly past top dead center .It could be almost top dead center on a slow running engine like a john Deere ,or say 35 degrees on a two cycle running say 17-18000 RPM .It's not that the piston speed is out running the spark it's you can't get the expansion to get going on the fuel .

Offline Al Smith

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Re: Chainsaw ignition timing
« Reply #13 on: October 17, 2016, 05:52:27 am »
Another thing which is only the theory but it bears an explaination . An magneto  ignition coil generates AC voltage but since it is only on the positive side of ground it's called pulsating DC .

It has the same sinosoidal wave form as AC .The trigger device fires the coil when it detects a negative transition in the wave form by an assortment of transistors ,capacitors and a bunch of electronic gooblede goo .

Nice to know info maybe but for all intents you can't do much with a solid state coil other than replace it if it doesn't work .

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Re: Chainsaw ignition timing
« Reply #14 on: October 17, 2016, 11:28:02 am »
"I have never seen a timing problem on a saw like you are talking about especially with two different coils."

Neither have I --and I have worked on small engines for over 50 years.


Over 50 years.    I would say the problem is something else other than the coils.   
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Offline RoyM

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Re: Chainsaw ignition timing
« Reply #15 on: October 17, 2016, 12:36:07 pm »
Hey, I resemble that remark. >:( :D :D :D I had a Remington Mitey Mite (yeah I know ::)) give me fits, no spark. Changed the points, nada. Changed the coil, nada. Installed the ignition from a running saw, still no joy. Installed ignition from dead saw on other unit, worked fine.
Threw it on the shelf until the customer started complaining.
For some reason I had the bar and chain off, I was pulling the rope and noticed the clutch was turning BACKWARDS. Somebody had assembled the F-M rewind incorrectly.
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Re: Chainsaw ignition timing
« Reply #16 on: October 17, 2016, 12:38:59 pm »
Hey, I resemble that remark. >:( :D :D :D I had a Remington Mitey Mite (yeah I know ::)) give me fits, no spark. Changed the points, nada. Changed the coil, nada. Installed the ignition from a running saw, still no joy. Installed ignition from dead saw on other unit, worked fine.
Threw it on the shelf until the customer started complaining.
For some reason I had the bar and chain off, I was pulling the rope and noticed the clutch was turning BACKWARDS. Somebody had assembled the F-M rewind incorrectly.

Now that is funny.
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Offline dannyupsolate

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Re: Chainsaw ignition timing
« Reply #17 on: October 17, 2016, 01:05:48 pm »
great thread ;D  other day I was reading a mastermind post where he filed of 20 thousandths off the key to advance the timing on his hotrod saw. my customers ms250 is still breaking pull ropes and damaging starter fingers. if I file 10 thousandths off other side of key to retard timing a little reckon it would tame this saw a little.

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Re: Chainsaw ignition timing
« Reply #18 on: October 17, 2016, 01:28:43 pm »
great thread ;D  other day I was reading a mastermind post where he filed of 20 thousandths off the key to advance the timing on his hotrod saw. my customers ms250 is still breaking pull ropes and damaging starter fingers. if I file 10 thousandths off other side of key to retard timing a little reckon it would tame this saw a little.

Yep it would but just put it back to stock.     I have a few saws also that I have advanced the timing on and you really have to pull them with conviction or else it pulls the handle right out of your hand.   But at the higher RPM's they sure do run.
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Offline dannyupsolate

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Re: Chainsaw ignition timing
« Reply #19 on: October 17, 2016, 02:36:49 pm »
this saw is stock but I have put 3 ropes and 2 starters on it this year. it belongs to a homeowner that only uses it once a month or so. it runs great but to rough on starters.

 

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