Author Topic: Echo 3900  (Read 3010 times)

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Offline Cut4fun .

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Re: Echo 3900
« Reply #20 on: September 11, 2012, 11:30:05 am »
He can look up stuff on the Internet just like you can and he can do it right there at the counter because he and I have done it before.

So now he just lied to me on the phone. Another reason I wont ever step foot in his place.  ;)
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Offline Cut4fun .

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Re: Echo 3900
« Reply #21 on: September 11, 2012, 07:33:45 pm »
I had no retro fit coils on hand that would come close.

I'm thinking something in a echo trimmer blower etc may work.

Here is a look at the 3900 coil.








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Offline Cut4fun .

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Re: Echo 3900
« Reply #22 on: September 11, 2012, 08:57:06 pm »
Coil part # 15660137330

Pretty neat read I just stumbled on.


The Echo CS-3900 Chain Saw ignition coil [module] has an armature and is U-shaped with two ends [sometimes three ends] facing the flywheel. The coil also has two sides. The primary side has thick wire wrapped around one leg approximately 150-200 times. The secondary side has very thin wire wrapped around the primary windings approximately 20,000 times. The flywheel has two imbedded magnets, a north and a south pole. When the magnets pass the U-shaped iron cores on the ignition coil, the primary winding builds voltage up to approximately 200 volts. Then, the electronic control module trigger breaks the current and sends it to the secondary side of the coil building voltage up to 20,000 volts used to fire the spark plug.

The Echo CS-3900 Chain Saw ignition chip is a trigger device that determines when the coil needs to fire the spark plug. It works by breaking the current from the primary side and sending it to the secondary side of the coil. This transfer steps up the voltage to fire the spark plug. The ignition trigger replaces points and the condenser on most chain saws having just two magnets [north and south]. If a flywheel has more than two magnets, then the ignition chip trigger will not work.

Note: On Stihl models 031, 032 and 041 these coils have a spark advance built into them and the ignition chip will cause misfiring.

To test the Echo CS-3900 Chain Saw ignition coil, disconnect the ignition switch wire at the ignition coil. Using a good quality spark tester, pull the starter rope with a good fast pull and check for spark. Removing the spark plug makes this process easier since it reduces the resistance when pulling the starter rope. If no spark is visible, remove the Echo CS-3900 Chain Saw ignition coil and sand the bottom of the coil. Also sand the mounting surface where the coils are attached to ensure a good and proper grounding of the ignition coil. Note: On some saws, the ignition coil bolts onto a plastic housing with a ground wire running to the cylinder or crankcase for a ground.

The high voltage from the ignition coil travels through an insulated spark plug wire to the terminal on top of the spark plug, then travels down the electrode threw the porcelain insulator to the ground electrode which is connected to the metal bottom body of the spark plug and is screwed into the cylinder.

Spark plugs can either have a metal gasket to seal the spark plug to the cylinder or a taper spark plug to seal the spark plug to the cylinder. The heat from the Echo CS-3900 Chain Saw spark plug is dissipated to the cylinder to help keep the spark plug cool.
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Offline Cut4fun .

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Re: Echo 3900
« Reply #23 on: September 12, 2012, 05:46:47 pm »
Found a used coil today on a shelf  of a used parts guy I know ;D    and now she has fire and runs.   8)


Sorry. I got your hopes up.  The saw I have is missing the coil.

I'm still needing the on/off switch (my poulan one wont fit) and a air filter.

Also what bar and chain pitch are you running on yours?  I havent removed clutch to check rim for sure but it appears .325 on this one. I would have thought 39cc would have been 3/8LP.
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Offline rockyridge

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Re: Echo 3900
« Reply #24 on: September 12, 2012, 11:44:50 pm »
I just bought 2 new chains at the Stihl dealer today - 91VXL56E - 3/8 050 56 links.  Took me for $21.50 each  My Echo dealer is 100 miles away and I very seldom get up there.  He charges me $1 an inch, so it'd have been $16 from him...

My 345 runs .325 chain.  All the rest run 3/8 - Two 3900s - 16", 6700 - 24", and 8000 - 36".

Offline Cut4fun .

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Re: Echo 3900
« Reply #25 on: September 13, 2012, 09:22:25 am »
This 3900 is set up for 325.   I put a b+c on it with a poulan foam air filter over carb intake.

I found a online echo parts dealer right here in Ohio. I got me a air filter and switch on the way. 

Original AF list NLA with superseded #, I then looked up that number it was NLA with another superseded number. This # showed up as the replaceable AF for 3900 and available $12 plus shipping. We shall soon see if it fits. 
Switch was $6.
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Offline Cut4fun .

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Re: Echo 3900
« Reply #26 on: September 13, 2012, 09:48:20 am »
Bar mount is K041

The IPL list only 2 b+c combinations on it.   This one has 18" in 325 and I might be changing it to 3/8LP.

16" 33SL 66     bar 16AOAD3366

18" 33SL 72      bar 18AOAD3372 

rockeyridge could you check your rim sprocket or spur for the tooth count. I wonder if you have a 3/8 7T  rim on it.
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Offline rockyridge

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Re: Echo 3900
« Reply #27 on: September 13, 2012, 11:46:25 am »
I'm not exactly showing much promise on giving good info here.  I looked again and it is .325.  The receipt I looked at at 11 pm last night was wrong.   Now I'm curious what the 345 is because it's a lot lighter chain than the 3900.  The 6700 and 8000 are 3/8, I'm sure.

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Re: Echo 3900
« Reply #28 on: September 13, 2012, 11:52:37 am »
Todays chains are normally  3/8LP  Low Profile aka Picco usually on the smaller saws, .325, full 3/8 like on your 8000 6700,
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Re: Echo 3900
« Reply #29 on: September 13, 2012, 01:24:04 pm »
Wow now that is customer service from the online echo place.  I received a phone call that the switch would have to be back ordered and it was looking like 2 weeks out date to get in right now. Then after that I received a email stating the same and they wanted to know what I would like to do next.

I called back and decide to drop the switch and ordered another part instead with my order.   They will get my echo business from here on. Right here in Ohio too.  ;D


So after that I decided I would make my poulan 3400 switch work in the echo.

 Opened up ground wire O that switch goes through and the plastic housing where switch goes through.  All done and works like a charm.




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