It's really looking like the Carb or the Coil could be the culprit, it comes down to a coin toss on which one to try first. Probably try the carb just for the sheer fact the the saw sat around unused and thus probably gummed up. That and the fact that the saw has extremely low hours so I would hope the coil would still be sound. Unless it was just lemoned from the factory.
Hi I know this is a pretty old post but figured I would give it a shot. I am having a very similar issues to yours.
. New top end, crank seals, fuel line, fuel filter, impulse line, vent seems to be working properly. Rebuilt the carb with walbro kit and still the same issue. All parts are OEM. Mine has the old style HD16 carb, not the HD16C. I also did vac and pressure tests that seem to hold indefinitely. Tested tank, fuel line and carb also.
It will seem like it tuned ok then all of a sudden it acts up again. Sometimes I can hear it happening and catch it but not always. Almost sounds like its running out of fuel, but I will richen it up well past where it should be and still does it.
I was hoping to find out if you fixed yours and what it was. Any help would be greatly appreciated. Thank you in advance!