Ht56 C

[bertsmobile1]

When I get into these situations I instal a spark tester or Colour Tune
Clamp the saw by the bar making sure it can not move ( some times I also support the engine end with a stand
Then it is a case of starting the saw & watching the spark tester
Some times I even video it so I can play back at a slower speed
I am looking to see if it stops sparking then stops spinning or sparks all the way to shutdown
If the former then the coil & wiring is suspect
so the next step is to unplug the coil at the coil to see if it is the coil or the wiring/switch .

If the latter then I know it is a fuel problem

 

[StarTech]

It also can a compression problem. I just ran into a similar problem with an old FS40. You could start it and run it holding the throttle open (labored at full) but as soon you let up to idle it would die. Further tests indicated it compression had dropped to 90 psi which is what I have found over the years to be too low as most 2 cycle units here requires 100+ psi to idle right.