My w3 ignition (for a 4 year old 3W 100) was giving me intermittent failure. This was happening after long flights - about 15 minutes into a flight. I bought a DA ignition, just to try something different. It works fine. Also very expensive (in the same ballpark as the 3W ignition). Dave at DA says the 3W and DA ignitions are of similar electrical design, but with minor changes to packaging and cooling. I think I had to change a connector between the DA ignition and the 3W sensor. I did not buy a new sensor, just the ignition module itself. So I am now using a DA ignition module with a 3W sensor. Everything has been working fine for a few months now. Actually today my 3W was running bad, but I don't have any reason to blame the ignition.

When you bench test an ignition, make sure the plugs are plugged in tightly to the ignition caps. And you must swing the prop pretty quickly for the sensor to trigger. Some ignitions will "trigger" using a hall effect transistor which will trigger at very low rpm'.s The sensor that DA and 3W use are not hall effect, but rather a coil technology. It takes a pretty good swing to trigger them. Once I thought I had a bad ignition, when it was merely a weak swing of the prop. the spark plugs do not have to be grounded to the case of the engine (like your lawnmower) because the circuit is completed through the metal shield around the outside of the ignition wires.