What is the gap on the coil on a sthil fs38

If this is a stihl saw....they are notorious for bad electronic ignition, as evidenced by blackened plug (weak coil).......Replace coil assy. and hold an air gap at the magnet on the Flywheel by placing a business card between the magnet and the coil assy. while tightening the bolts on the coil....This air gap is critical so be careful that the flywheel is not contacting the coil assy. attach the small wire to the coil for shut down function.........

Possibly grass wound around the shaft behind the trimmer head, remove the trimmer head and pull out any grass debris, chech for grdryed grass behind the driver flange.

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

W H a c k e r not wacker
wack
wak/ USinformal
adjective
adjective: wack
1.bad; inferior.
"a wack radio station"noun
noun: wack; plural noun: wacks
1.a crazy or eccentric person.2.worthless or stuupid ideas, work, or talk; rubbish.
"this track is a load of wack"Origin
1930s: probably a back-formation from wacky.

whack
(h)wak/ informal
verb
verb: whack; 3rd person present: whacks; past tense: whacked; past participle: whacked; gerund or present participle: whacking
1.strike forcefully with a sharp blow.
"his attacker whacked him on the head"North Americanmurder.
"he was whacked while sitting in his car"noun
noun: whack; plural noun: whacks
1.a sharp or resounding blow.2.a try or attempt.
"we decided to take a whack at spotting the decade's trends"3.British
a specified share of or contribution to something.
"motorists pay a fair whack for the use of the roads through taxes"Origin English thwack

if you went to the sthil pages I referred you to , there is one for a chain saw coil that has a spade terminal on the coil
as most coils would be the same I would put that spade fitting on the coil and the other terminal under a mounting bolt
remove the spark plug and pull the cord and see if the spark is at the plug gap
check that the system is switched on first

Have checked your spark arrestor in the muffler?

u got spark put a dime in the plug that's the gap u need hope this helps or just a bit of gas into the head where the plug goes good luck

you can only adjust the coil to flywheel gap... timing for the flywheel is preset and un-aqdjustable

Do you have a good spark.? Is fuel getting into the cylinder and making the plug wet.? Im assuming the compression is good.

remove the recoil cover and check the dogs that engauge the starter to the flywheel