Reply To: '65 BigTwin 40hp 1/2 spark

[Don]

Again, I love the nice neat and clean job you have done on that mag plate…. OK, so the borrowed mag plate assembly sparked on both cylinders…But, yours, even with all new OEM pieces refuses to spark on one cylinder….I am assuming it is always the same cylinder that refuses to spark, correct? I’m not that familiar with what the underside of an RD mag plate should look like, in terms of wire routing and clamping. I’m hoping someone will examine your nice pictures closely and see something….
Let’s back up a bit and review for me….Did this thing spark on both cylinders before you set out on this frustrating ignition project? Or, is this an engine that you just acquired, and you decided to service the ignition system….
You have replaced both plug wires with no change, correct? I find it hard to believe that the same possible bad connection has repeated itself every time creating the same issue. The only other thing I can think of at this time has to be some issue that has a way of repeating itself no matter how many times you pull this thing apart….
Perhaps, there is some sort of issue with the routing/clamping of the plug wires under the mag plate which is grounding that plug wire to the mag plate every time you reassemble this thing. Try holding the mag plates side by side so you can compare wire routing/clamping between the two mag plates. I would then remove the problem plug lead one more time (sorry) and have a real close look for pin holes in the lead or damage from clamping that might be grounding it….
If all this reveals nothing, then I would simply route a plug lead directly out of the coil and out from under the mag plate (no clamping or routing under the various pieces), then recheck for spark on that cylinder…..