rcj8y has a built in resistor to protect electronic ignitions from spurious signals also to reduce interference to TVs etc.
i.e. the R in the plug designation indicates resistor.
Yes you can use a CJ8 for a CJ8Y, but you cannot use a CJ8Y for a CJ8......the CJ8Y has about 1/4in more thread.
ngk BPMR4A
recommend .030 "
Cj8y
3/4
NGK BPM6A
an rc8j resistor or a cj8y
Champion RCJ8Y. Very common plug for smaller 2 cycle engines. Champion RCJ8Y. Very common plug for smaller 2 cycle engines.
Champion CJ8Y
The correct spark plug is a Champion RCJ8Y.
Tecumseh Part #611049 - Champion Spark Plug #RCJ8Y
3/4 inch socket - .030 gap