Hi, which make and type of spark plug should I use in my Manx M40 350cc 1961 shortstroke engine ? In a manual I have a Champion NA19 is listed, but my suppliers just shug their shoulders ? Would like to hear what make and type you are using and has anyone any experience with iridium type plugs ?
thx,
Peter
Ken McIntosh
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I use NGK Gold-Palladium racing plugs with a fine wire centre electrode.
These have a normal type earth electrode, rather than the side electrode of the old type racing plugs.
This makes them less prone to oil or fuel fouling, and will work OK in a Manx.
The range is from a "#8" (B8EGV) to "#11" in half steps (ie #10.5). The higher number the colder the heat range of the plug.
For gasoline I recommend a hot grade (B9EGV) for short tracks where full throttle is not used much, to a cold plug (B105EGV) for fast tracks like Daytona where full throttle is held for long periods.