Topic: Spark at Dyna Coil

[pmpski_1]

I just installed a new set of Dyna Coils and plug wires on my 74 550. I got everything set up and started to go through testing the spark at the plug by grounding it on the engine block and cranking the starter.

When one of the plugs was out of the cylinder (#4), turning the ignition key on caused a big spark to jump from the plug wire where it connects to the coil to the screw that attaches the black\white wire to the coil.

When I put the plug back in, there was no longer a spark at the coil when the ignition key is turned on. I had to leave and did not get a chance to test another plug wire to see if it did the same thing.

This seems strange that this happens, but I am still pretty new to the electronic side of the bike. It was a strong bright blue spark coming through the rubber end cap to the screw. It only sparked when I turned the ignition on. Is this expected when the plug is out of the engine, or did I hook something up incorrectly?

Thanks in advance.

[Steve F]

It sounds to me that you have a bad plug wire insulating boot at the coil.  There shouldn't be any spark arcing while the plug wire is installed correctly. Remember that electricity is lazy, and will take the shortest route to ground whenever possible.  In this case it's from the coil directly to the closest place to sink to ground, which is why you didn't have this arcing problem when you put the plug back in the wire.   Be sure the plug wire is on the coil all the way, and there's no cracks in the rubber boot.  If you get a spark when you turn on the ignition, that just means that the points are making contact, and you get current flow to the coil, which will produce a spark.  That shouldn't be anything to worry about.