When using data recorders or memory tachs it is essential to "shield" all of their associated wires from the magneto and ignition (spark plug) wires. The powerful radiation & electro magnetic forces emitted by the magneto and ignition wires will interfere with the proper functioning of a data recorder. The user, when encountering trouble, may call the data recorder manufacturer and their standard answer to cure all woes is " change to suppression type ignition wires".
This is really not a satisfactory solution and you shouldn't do it. Performance will be adversely affected by suppression wire. Suppression wires runs 30 to 50 ohms resistance per foot. A standard wire runs about 1 to 2 ohms resistance. The goal is to achieve the most powerful spark possible at the plug gap. Using suppression wires defeats this goal.
The answer is in shielding the data recorder from the electronic field emitted by the ignition wires and the magneto.
Commercial braided shielding is available at good electronic stores and can be used to shroud the data recorder and its wires. Even a simple aluminum foil shield will help suppress the radiation & noise. Shrouding the ignition wires in braiding will also help to eliminate the magnetic noise radiated by the ignition system.