Ok, I have tried to do some searching and have read all the info I have on these mowers but I can not find the champion, or ngk or anything part number for the correct plugs for these mowers.
From memory I used champion L90C plugs, I bought a carton of them when bunnings put them on clearance, although it was a long time ago now. Cheers Joe.
The twin I have just got had a J11C in the front and a CJ8 in the back. I assume the CJ8 is incorrect. I just checked one of my lightweights and it has a J8C.
My guess is almost any plug with a long shank and a short thread should be ok?