Color of spark plugs
 

https://cimg1.ibsrv.net/gimg/www.rx7...d2587fa83.jpeg
Top plug front rotor
https://cimg3.ibsrv.net/gimg/www.rx7...e580f93cd.jpeg
Top plug rear rotor
https://cimg4.ibsrv.net/gimg/www.rx7...08efe9f6c.jpeg
Cold compression front rotor
https://cimg5.ibsrv.net/gimg/www.rx7...724877b24.jpeg
Cold compression rear rotor
https://cimg7.ibsrv.net/gimg/www.rx7...e36c6cd6f.jpeg
Hot compression front rotor
https://cimg8.ibsrv.net/gimg/www.rx7...a8d9d2460.jpeg
Hot compression rear rotor
Hey guys

General question about spark plugs.
I have an fd from 1996, previous owner had it rebuild 20.000kms ago with practily everything new and a large streetport. I premix about 4,6ml per L of fuel, i don’t know how much that is in mpg. Now today i did a compression test and i noticed that my top 2 plugs where pretty diffrent of color, now im wondering wich one is “good mixture” and wich one is “lean/too rich”. The cleanest one is from the front rotor and the black one is from the rear rotor. I’ll also add in the compression numbers if it’s any help. Higher numbers are from front rotor, lowers are rear rotor. Also is it normal to have that big of a diffrence (10psi) between the front and rear rotor after 20.000kms and even between hot & cold motor?

welcome to the board. :)
my first question would be what did the lead plugs look like?

if you join these threads/conversations, maybe you can get your questions answered.

https://www.rx7club.com/2nd-generati...-plug-1163645/

https://www.rx7club.com/general-rota...otors-1090077/

Hey

Thanks for the answer, i didn’t take the lead ones out but by reading the threads you linked it looks like all should be fine. Plugs can get those colors because of the oil pre mixed with it. The compression numbers are something else, apparently streetporting should not affect the compression numbers because the compression is messured at the spark holes and the rotor is not at a point that the inlet or exhaust ports are in the chamber of the compression messured. So i think it might have been not rebuilt properly i guess..

Bryan