Spark Plug Setup Various Cylinder

"Hot" and "cold" Spark Plugs

It is of paramount importance to secure the correct spark plug fitting the individual engine setup. The basic parameter you have to be aware of when running a Vespa engine is the so called heat range specification. Operating the engine under certain erroneous conditions may result in piston damage or a badly performing engine regarding power, idle and consumption. The technical term "hot" for a spark plus is used when the tip of the spark plug can keep more heat, when it basically is a better heat insulator. The technical term "cold" for a spark plug is used when the heat is more easily conducted out of the spark plug tip, when the spark plug tip is basically kept at a lower temperature. That is what is known as the heat range of a spark plug. It is typically specified as a number, whereas different manufacturers are using different methods in order to specify the heat range of their spark plugs. For example: Bosch uses higher numbers for "hotter" spark plugs (W5AC) descending to lower numbers for the "colder" versions (W3AC). Some other manufacturers using ascending numbers from "hot" spark plugs up to "cold" spark plugs. As a principle you should remember that modified or especially racing engines as well as long distance runners require a "colder" spark plug than compared to the genuine engine setup.
The following table and information is mainly taken from 3 major sources. My favorite here was SIP Scootershop:
Cylinder Type and Spark Plug Specs
Brand Comparison Spark Plugs SIP
Brand Comparison Spark Plugs Motorradlädchen
It may for sure be possible that one vendor recommends one type of spark plug for a few different engine setups. Whereas another manufacturer is recommending another spark plug spec type. There are of course indidvidual differences per the specific manufacturer.