I have a DA-100 and have checked the spark simply by placing the plug into the cap, and grounding it to the engine while the prop is flipped at starting speed. The instructions are ambiguous: they say: "unless you are having problems, don't bother "testing" the ignition with the plug removed from the cylinder". They don't say "don't do it, because doing so will harm the ignition".

In your case, you are having problems: Test it. I do it all the time with my various engines, all with C&H ignitions, and have never caused a problem that I know of.