What type of spark plug and fs45 stihl trimmers work with

hi try here hope it helps https://www.scribd.com/doc/190134377/FS45-Service-Manual

A hard pull on that unit would indicate a sheared flywheel key. The key is part of the flywheel. Check to see if there are 'rub or scrape' marks on the outside of the flywheel. Adjust coil clearance to .010". Coils on those models are normally very reliable. Use a spark tester for lawn mower engines. Preferably with a light in the center of the tester wire. If it its an adjustable tester, adjust the gap to at least .065 to 0.85". The light tester should produce a bright orange light, the adjustable tester should produce a bright blue spark. I cannot find specs on those models, as dealers use the 'light in wire' type tester.

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

most times it is easier to do just that

over fueling

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Yes it could be.You can purchase an inline ignition tester from your local parts store and test it. Its also possible the plug is fouled.

Check the timing gap between the ignition module and the fly wheel.

No, I'm not sure why STIHL even makes curved shaft trimmers at all. I have never worked on ine in 10 years of being a STIHL tech, I just throw them out when they don't work and steer the customer to a straight-shaft. It's their punishment for the mistake of buying the curved shaft in the first place.

This model is the closest this site comes to the model you have. it should help as diagrams should be in the manual on later pages. You will need Adobe Acrobat Reader as the manuals are in PDF form:
http://lawnandgarden.manualsonline.com/manuals/mfg/stihl/fs_55.html
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