plugs and gap

I have found that when you buy plugs for an application they are often pre-gapped for the given electrode length It is important to keep the electrode and ground gap parallel for good wear life. If the gap is increased significantly, the ground electrode becomes short, and the gap is a wedge shaped. So if you buy a plug that has an original gap of 0.040", going to 0.060" may be a detriment.

As the gap is increased the spark duration decreases because energy consumes faster with increased voltage. MSD CDI has a short duration to begin with, that is why multi spark happens at lower RPM.