Latest acquisition: 041 Farm Boss

If I decided to try fixing the original ignition, it occurs to me that I don't know how I'd get the gap between coil and rotor correct since the coil sits *inside* the flywheel. And then there's the problem of setting the timing...

 

That is a really clean saw - and the original bar scabbard to boot

Sounds like you're on the right path with the coil. An intermittent open within the coil will show open, but the high voltage can bridge the break. This is when a Meggar/voltage inducing insulation tester is nice to have laying around

 

The kill switch is on the primary side of the coil and if it is chaffed can cause the primary induced voltage to trickle to ground. Or if not fully open(probably has to have 1 megaohm or greater to function) will collapse the primary field and give weak spark.
When you checked the secondary coil, the resistance from the plug boot to ground is where you should be measuring - if that is open "OL"(assuming you are using a DVM, otherwise the highest range setting on an analog meter). Some meters will have maximum resistance measurements, basically show OL at some specified value - like my Fluke T5-1000, it's limited to 1000ohms.
I checked mine with it and it's OL(I can get some reading with my 187 when I get back to work on Wednesday). Juts wanted to make sure the meter you're using is reading in the correct range before you start changing parts.

Here's the easiest to understand video of magnetos, points, condensers I have ever run across.

 

I checked the secondary with the kill switch completely disconnected from the condenser to eliminate even the possibility of an unseen short in the wire. I was checking the secondary resistance correctly, but I'm not sure about the limitations of my meter which is just a Radioshack cheapie that has seen better days. A neighbor has a nice Fluke meter he will lend me, but he's out of town today.

Thanks for the video. I'll watch it shortly.

 

Thanks, that is a really good video, and it reminds me (off-topic from the 041) that I am even further from understanding the 2-part ignition systems in some older Husqvarna saws. Can you shed any light on the functions of the two components in those?

 

From what I gather the two piece has a primary & secondary coil and the smaller "control box" is the gating/firing/triggering coil with an SCR/transistor(I believe). It's an electrical make/break switch that turns on when a voltage is applied to it - it's gets this voltage from a small coil inside that box.
If you look back in that video ~10:00min mark, that's how newer ignitions are made now, the small coil is built into the main coil.
It was probably something Husqvarna did to get away from points initially, and it allowed them to move the triggering coil and adjust timing.

 

Well, I procured a good clutch and fanwheel, and got the ignition working again. I thought I might get it running today, and it did kick over a few times on a bit of gas I dropped into the intake, but it wouldn't keep running. Fuel and impulse lines seemed to be in decent shape so I decided to pull the carb and see whether it seemed to need rebuilding. When I took the carb off I could see into the intake, and discovered that the saw had at some point ingested something very hard and sharp, which had bounced around in the intake port and cut several deep gouges into the piston. All the damage had occurred low on the piston and below the intake port on the cylinder, so it didn't affect compression and would probably still run, but I don't want to put it back together like that.

I'm debating now whether to go with the next-cheapest repair, which would be to soften the edges of the cylinder scratches as much as I can and reuse it with an aftermarket piston for $20. The gouges in the cylinder are small but deep and ragged, though. Decent used top ends are common and seem t0 start at about $85, while new OEM pistons OR whole aftermarket top ends are about $110.

Considering the fine exterior condition of this saw, it's amazing how many internal problems it has. If I were smart I'd part it out, but that seems such a shame...

 

Bummer.

 

Ouch. If mine, I don't think I'd try doing much to the cylinder. Perhaps shelve it for a bit and look for a deal on a parted out cylinder on the bay? Or, cut losses and part out - but I can see the lure in getting the old girl running again. Cheers!