Stihl FS 45 No Start

[EricSER]

I want to start off with hopefully this is the right area to post this thread in and if not I apologize. If it needs to go somewheres else please let me know.

I’m a starting novice at small engine repair and I was given a Stihl FS 45 string trimmer to repair. The issue was that it wouldn’t start. I got it home and have done the following to it: replaced fuel lines, fuel filter, carburetor, and air filter. This has made no difference in getting it to start.

Since I’m a beginner at this I didn’t check the spark until after I did all of the above. This is when I realized that I can’t see a spark when I have the plug rested on the metal head of the trimmer. After putting in a spark tester I do see a spark in that but either I am blind or it isn’t sparking at the plug. I have tried a different but same type of plug from a leaf blower that works and I still can’t see a spark.

This led me to the ignition coil but I can’t find a replacement for the module/coil that is installed on this trimmer. Honesty I’m not even sure if I am on the right track here as far as diagnostics.

Does anyone have any ideas of what I could try or is there something I missed, did wrong , etc?

 

[DND 9000]

Check all the wires, maybe there is a short circuit. Also remove for testing the kill switch cable on the ignition module and see if you have a better spark. Did you check the gap between the flywheel and ignition module? Should be "0.012 in. If it`s to large you don`t have a good spark. A other reason could be a sheared flywheel key and therefore the spark may not be strong enough or is out of the right timing.

Please elaborate exactly on your version of the FS 45. (year of manufacture, serial number etc.) There are 3 different ignition modules, depending on the age and the exact version. There are some things to consider and restrictions which are importand, but we need more input from you.

 

[EricSER]

Check all the wires, maybe there is a short circuit. Also remove for testing the kill switch cable on the ignition module and see if you have a better spark. Did you check the gap between the flywheel and ignition module? Should be "0.012 in. If it`s to large you don`t have a good spark. A other reason could be a sheared flywheel key and therefore the spark may not be strong enough or is out of the right timing.

Please elaborate exactly on your version of the FS 45. (year of manufacture, serial number etc.) There are 3 different ignition modules, depending on the age and the exact version. There are some things to consider and restrictions which are importand, but we need more input from you.

On the ignition module are both cables from the on/off switch refereed to as the kill switch cable or just one of them? I'm assuming you want me to disconnect both but I want to be sure. Unfortunately, I don't believe I have the means to check the gap for sure but I have reinstalled the module using a business card to set the gap.

It looks like the M.D. is 11/08, serial I'm not 100 % on but it does have the following numbers 4140-011-2381, 8 00 413 725, engine family 8A8XS.0274RY, and 4140 967 3405 A S. It is also labeled as a FS 45-Z Brushcutter, Autocut 5-. The serial number on the ignition module is Stihl 4140-1306A 0831

If there is anything else I can provide or do I am happy to do so. I appreciate your help!

 

[DND 9000]

Thank you for the information. No it should be the 2 cables that go from the ignition module to the switch. The part no. of your current ignition module is 4140 400 1305. That version is discontinued and was replaced by 4140 400 1308. Your serial no. is 8 00 413 725.

 

[EricSER]

Thank you for the information. No it should be the 2 cables that go from the ignition module to the switch. The part no. of your current ignition module is 4140 400 1305. That version is discontinued and was replaced by 4140 400 1308. Your serial no. is 8 00 413 725.

Okay, I will disconnect those cables and see if that makes a difference for the spark.

Originally I did order a replacement ignition module on ebay but I could not get it to fit without hitting the flywheel. I believe it indicated the model 4140-400-1308. Was that just me doing something incorrectly and it should have fit?

 

[DND 9000]

Normally that should fit, it`s a direct replacement part.

 

[EricSER]

Normally that should fit, it`s a direct replacement part.

I wonder if the issue is that this is a aftermarket replacement and not the OEM stihl replacement. I would think it would still fit but maybe I did something wrong.

I will try disconnecting the kill switch first thing in the morning. You mentioned a sheared flywheel key; how would I check that?

 

[DND 9000]

The key on this flywheel is inside the flywheel, not a extra part as on some chainsaws. You would have to remove the flywheel to see if it is sheared.

 

[EricSER]

Just wanted to provide a final update to this thread. The 4140 400 1308 ignition module from Stihl fit my trimmer perfectly and I now have spark. I'm guessing the version I ordered on ebay that listed the 4140 400 1308 part number was just some cheap knock off hence why it did not fit. I have not reassembled yet to make sure she runs but I expect her to now.

Lesson to be learned here is to not order cheap parts on ebay.

 

[DND 9000]

Thank you for the final report.

 

[EricSER]

Thank you for the final report.

Thank you for your help!