One guy at the field was getting glitches. Found out he took the ring off the bottom of the plug cap because it was hard to put on and off. Put back on and got a good ground everything was good. Another guy was getting glitches on a Quadra 35. Turned out he had a lawn mower plug in it. Gave him a Champion RCJ7Y and everything settled down. Another, when the shielding on the plug wire was grounded to the motor, the glitches would stop. The shielding was not attached to the plug cap.
Food for thought.

Gord.