Small Engines (Lawn Mowers, etc.): Stihl HS45 hedge trimmer wont start, air gap, exact specs

Question
My Stihl HS45 hedge trimmer won't start. At first I was getting no spark to the plug. I replaced the coil/mag and set the air gap to about .018. I do not have the exact specs on where to set the gap but this was a guess by using the business card method as suggested by others. I now have spark but it won't start. When trying to start it it will pop back through the carburetor once or twice but will not run. Is this some sort of timing issue and if so how do you set the timing? Thanks Dennis

Answer
Stihl made a change to the HS45, and they changed the coil and
crankshaft, as the keyway holding the flywheel is what keeps it in the correct position.  You need to take the whole trimmer back to the
dealer that sold you the coil, and make sure they sold you the correct one.  the old coil # is 4140 400 1300, the new one is
4140 400 1302