@Stump Shot is the 5mm spark jump the end all test? Cuz swapping them around and trying to feel which ones run best sucks.
Yes and no depending on how you are looking at the issue.
If it won't jump a 5mm gap, OR is not a bright blue color(white/pink/orange or light pale blue) making an audible snap, it's junk.
There are other tests, it could be ran on a Merc-O-Tronic 79 tester and see if it pass/fails.
Rotary makes a simple two colored neon tester that works pretty good, otherwise most all other testers are 5mm.
Note on 266/670 two piece coils, when one goes out(original) the other should be replaced at the same time as it will fail shortly after.
Don't waste your time with Chinese coils even if they spark(weak) they won't for very long. There were some out for a while made by Magnetron in South America, these were good units. Otherwise pay the man at the Husqvarna counter what he wants and be done with it.
I have a pile of old 2 piece 61/266/630/670 coils and triggers that are junk. Even when resurrecting an old saw they just seem to fade out and quit having not given much service. Just seems the age has caught up with them.
They are not like 281/288xp type 2 piece setup, those seem to go on near forever it seems like and rarely go bad.
Another note, if when replacing coil and trigger nothing seems to work, check the flywheel by replacing with another. I've had two 266 flywheels go bad and make me kinda crazy trying to figure out what was going on. Just what happened to them I couldn't say. I've heard the magnets can be reversed possibly if it receives a hard blow to it.