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Help with Stihl FS 45 trimmer

Discussion in 'Mowers and More' started by GBertolet, Aug 10, 2019.

  1. GBertolet

    GBertolet New OPE Member

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    I am repairing a Stihl FS 45 trimmer for my neighbor, and I am stuck. The machine was sitting for some time, before it was given to me. There was no spark, and the coil tested shorted. I replaced it for $10 , and now I have spark. There was no fuel coming to the cylinder, and I replaced the carb for $10 also. I now have fuel in the cylinder. I cleaned the spark arrester also. It was pretty clogged. At this point, I have frequent backfires through the muffler when attempting to start. Occasionally, I have blowback through the carb also. I checked the flywheel key. It was beat pretty bad, so as a precaution, I found a used flywheel in decent shape and replaced it for $20. Still won't start and backfires. I have heard that sometimes the electronics in a coil are bad, but still spark, but the timing is way off. In the Stihl manual, it mentions this possibility. This sounds like what I am experiencing. Do I have to just buy another coil to see if my suspicion is correct, or is there a test? The coil I have now was a cheap import. Maybe junk to begin with. Any suggestions would be appreciated.
     
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  2. DND 9000

    DND 9000 Super OPE Member

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    It is possible that you have a coil with the wrong ignition timing. On aftermarket parts you never know if they are good or not. Please give us more specific information. Exact model of your trimmer, year of manufacture, serial number etc. What is written on your old oem ignition module? How is your piston looking, (inlet and outlet side)? You say you have spitback through the carb. A little bit is normal but not to much. A carb for $10 could be junk too.
     
    Last edited: Aug 11, 2019
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  3. Fish

    Fish Pinnacle OPE Member

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    Take off the muffler, then try it.
    Take a look at the piston while it is off as well. The exhaust port may be carboned over.
     
  4. GBertolet

    GBertolet New OPE Member

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    Thank you for your responses. I had the muffler off already, in preparation for a vacuum/pressure test of the crankcase. No leaks. No carbon blockages on the port. The info on the old coil is Stihl 4140 1303A MA-43-1982. The kill terminal was shorted to the core. The tag on the trimmer lists 4140-011-2301, SN 255823942, FS 45 Z Stihl Trimmer, 045-1016. I can't find a date of manufacture.
     
  5. DND 9000

    DND 9000 Super OPE Member

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    A new oem ignition module for your FS 45-Z would be the 4140 400 1308. But if it fixes your problem?
     
  6. GBertolet

    GBertolet New OPE Member

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    I had just done some more research. The 4140-400-1308 coil is for post 2001 FS 45 trimmers, and is incompatible with 2001 and earlier 4140-1303A, coil FS 45 trimmers, which mine is. The new replacement coil I had purchased, is a 4140-400-1308. If this proves correct, this is my issue. I will have to look for one of those old obsolete coils.
    https://www.greenacresmowers.com.au/ignition-coil-module-for-stihl-fs38-fs45-fs55-fc55
     
  7. Fish

    Fish Pinnacle OPE Member

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    The date of your trimmer should be on the sticker, if that is still legible.
     

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  8. Fish

    Fish Pinnacle OPE Member

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    Here is a pic of the 2008 price list.
    pl 001.JPG
     
  9. Fish

    Fish Pinnacle OPE Member

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    Here is out of the 2019 price list:


    4140 400 1200 FLYWHEEL $69.58


    4140 400 1304 IGNITION MODULE (MM55) $29.89

    4140 400 1305 Ignition Module MA-54 $34.63

    4140 400 1308 Ignition-module $29.89

    4140 400 1309 Ignition module $40.20
     
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  10. GBertolet

    GBertolet New OPE Member

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    I found a Stihl 400-1303A coil. Should be here by the end of the week. I will let you know.
     
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  11. Wonkydonkey

    Wonkydonkey Pinnacle OPE Member

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    I can confirm the backfiring is down to the wrong coil. I had it with a fs55
     
  12. GBertolet

    GBertolet New OPE Member

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    Fixed! The 1303A coil did it. Popped the first pull and started on the second. It's frustrating on how secretive Stihl is on product maintenance information. In 2002 Stihl went to the 400-1308 coil. This makes mine, a pre 2002 model. It's just dumb luck, that I stumbled on a narrative for an aftermarket 400-1308 coil, that said don't use this for a replacement for a 400-1303A coil, as they are incompatable. The average person would not have known this, and ultimately out of frustration, thrown this trimmer in the trash heap. Wonkeydonkey nailed it though. Thank you.
     
  13. Wonkydonkey

    Wonkydonkey Pinnacle OPE Member

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    Yeh, I had the fun of buying the wrong one, and had the same prob backfiring.

    The only reason I found out was I took/swapped it with another coil off some other trimmer.
    Then I found the coils were different. Because the backfiring coil work on the other older trimmer

    Your probs were really the same as mine...;) pleased you sorted it thou.
     
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