I generally use an ohm meter to check for continuity inside the coil. The coil is actually a transformer in that it has a primary and a secondary coil in it. The primary is checked from ground to the terminal on the back of the coil and the secondary is from ground to end of plug wire. Should read about 10 ohms on the primary and a few thousand ohms (but not open) on the secondary. If the coil has continuity and the saw runs bad I would check the condenser or points. If it is a solid state ignition you cannot check it this way, you should just replace it with a known good one.
