Thanks Gadge. I didn't realise there was so many. I have been told time and time again just wack a CJ8 in. So for the uninitiated what are the main differences in the above plugs? Wouldn't there only be one or two reach lengths?
There are actually three reach lengths; most are 3/8", but the L-14 is 1/2" and the N-21 is 3/4".
The CJ-8 and RJ19LM are 'compact' plugs; i.e. 3/4" hex rather than 13/16", and short body and ceramic insulator top. So the J-8 and CJ-8 plugs are functionally identical - same thread diameter, reach and heat range.
The other difference is the 'heat range'.
What this means:
One of the most misunderstood aspects of spark plugs is its heat range. It is believed by many that the heat range measures spark temperature or intensity. This is incorrect as the heat range is actually a measurement of the plug's ability to transfer heat away from the tip of the spark plug. One cannot change the temperature of how hot a fuel burns.
A hot spark plug has an insulator design that will be slower to draw heat away from the plug tip (thinner insulator mass), whereas a cold plug has an insulator design that will be faster to draw heat away from the plug tip (thicker insulator mass). For a spark plug to function properly it must have a tip temperature hot enough to invoke self-cleaning, while remaining cool enough to avoid pre-ignition.
Credit: NGK
The heat range rating of the Victa plugs is most easily read from the number in the NGK type designation - lower number = hotter plug.
Applications [to mid 1990's]:
N-21 - used in all early Victas up to 1960, and 'angle plug head' 2-stroke engines up to the early 1970's.
L-14 - only used in the Model 10 Series 'central plug head' 125cc 2-stroke engines of the early 1960's AFAIK.
J-8 - used in Kirby-Lauson 4-strokes through the 1960's to 1972.
CJ-8 - used in east-west mounted 125 and 160cc 2-strokes from 1970 on, and some [but not all] north-south mounts in that era. Also used in B&S engines fitted from 1972 on.
UJ-12 - used in some north-south mounted 2-strokes in the early 1970's, along with the 85cc Compact and 170cc Twin 2-strokes.
RJ19LM - resistor [to suppress radio interference] version of CJ-8, used in later model B&S and PowerTorque engines.
![[Linked Image]](https://www.outdoorking-forum.com.au/forum/uploads/usergals/2017/01/full-5630-32409-victa_plug_xref2017_01_24.png)
