Aftermarket spark plugs

Sorry Yoda, your link did not work.

Here is a few link 4 ya..........
http://motorbicycling.com/f30/bicycle-motor-spark-plug-755.html

http://motorbicycling.com/f3/e3-spark-plug-12976.html

http://motorbicycling.com/f13/killer-spark-plug-oil-10349.html

http://motorbicycling.com/f34/spark-plugs-12181.html

http://motorbicycling.com/f3/spark-plug-suggestions-11018.html

http://motorbicycling.com/f4/best-spark-plug-6681.html

Hey!! thats what I'm using the E3 Diamond fire -it says on the package (new tecnology)
-my 35 cc came with ngk bm6a which were easy to find,however my 48cc came with a torch that I could not find,basically the same plug but with different heat rating,however I was able to get it cross referenced to the champion cj8y-the store had cj8 but no cj8y
My E3.12 plug replaces Champion; CJ6,CJ6Y,CJ7Y,CJ8,CJ8Y,RCJ6Y,RCJ7YRCJ8,RCJ8Y
NGK ; BM6A,BM7,BM7A,BPM4A,BPM6A,BPM6Y,BPM7A,BPMR4A,
BPMR6A,BPMR7A
Ive got 4 spares in my tool box, anyway, from what I found, is that they work prettygood ,even though they say that these will last the life of the motor,my manual tells me to change them after every 50 hours, so thats what I do. :-/

I looked up our stock Z4C spark plugs and it looks to be a brand called: Sino
heres a chart for other plugs and the sizes of each.

Z4Csparkplug-BOSCH|WS8E-W20M-U-CHAMPION|CJ11-NGK|BP6L|BM6A

if you are going to a parts store. the plugs that fit these bikes also fit volkswagen beetles 60's through 70's