I'll do this one more time. Re-locate the ground to a stable location. The issue you are having has been all too common with people that have ground straps attached to the engine mounting bolts. Many have argued the point, they even do some other very odd things to attach the ground strap. Later they send the ignitions and/or the engine back for a "fix", only to find out when it's returned there's nothing wrong. Just their workmanship. Doesn't matter what type of engine it is. If the ground is improperly attached you will have glitching.