My father in law (aircraft mechanic, long time flyer) has a BT-64A (not the -EI with electronic ignition) and can't get any spark. The engine is near new and given up by the first owner because of this problem. He's replaced the magneto, the air gap is good, the magnets are still in the flywheel, but still no spark. With the plug out in complete darkness if he spins it fast enough with no compression he can start to see a little, but still hardly enough to even feel with your finger on the plug. It doesn't matter if the kill switch wire is plugged in or not, no spark. This was the same with the original magneto and the brand new one. What the heck could we be overlooking?!? Bad run on parts?

The magneto gap is to be set at the thickness of a busineess card

These kind always did need to be spun pretty fast to make a spark

Did it make enough spark to jump the plug gap?

A business card was exactly what he used. I asked him about it, rememering the 3x5" card rule I've always used with small engines, and he said he had used a business card.

He said with the plug out and spinning it pretty much as fast as he could he could barely get any flicker out of it, and when it did it was very intermittent.

Time to change over to battery ignition