i just picked up this fc not too long ago. and i decided to do a little tune up. so i changed the oil and changed the spark plugs. all 4 of my plugs were BLACK. what does this mean? is this normal or is something leaking or something. im not too good with rotaries obviously so any help would be nice.

 

carbon build up? not really a sign of anything as far as i know

 

our engines have oil injectors, all ur seeing is build up of carbon, like syritis said.
ur gonna go through plugs a lot more often then other cars.

what ur seeing is not anything to get too worried about, heres a good website to see
some different causes of plug fouling:

http://www.verrill.com/moto/sellingg...colorchart.htm

i would either buy them in bulk, u can catch deals sometimes that way, of get some FINE
grit sand paper and carb clean and go to town on them... speaking of which i need to do
the same lol

also, and not to insult your intelligence i just dont know how familiar u are with rx7s,
u can ONLY use spark plugs for rotaries.
ngk bur9eq are trailing (T) and bur7eq are leading (L)

hope i helped some

 

heres more plug info, if ur interested:
https://www.rx7club.com/showthread.p...trailing+plugs

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/can-same-spark-plug-used-trailing-tailing-880279/

 

lol non taken. i already looked it up before hand and i bought the right spark plugs. thanks for the input

 

nice informations, and one question from myself. How often do you change em?

 

Black (carbon buildup) is not particularly significant as others have stated. However, if the carbon buildup is on the center ceramic insulator (red area on attached image) that is not good since it provides a path for short circuiting the electrical charge away from jumping the gap to the other electrode and creating the spark.

 

but does it mean a particular problem wrong within the engine?

 

Running really rich usually.

You have to understand was someone mentioned earlier, our engines burn oil, and carbon is to be expected. Instead of doing 15k mile changes of my plugs, I usually yank them at 10k and clean them up with some carb cleaner/sand paper and toss them back in for another 10k miles.

After 20k the spark gap starts getting too wide and the electrode will start to get thin.

 

If the engine was flooded recently it is highly likely that the plugs will look disgusting like that.

 

If the car runs good don't worry about it. For peace of mind check them again next time you change the oil.

 

I am running 6 and 8s, not 7 and 9s on mine, starts like a charm. Only thing is, one of the trailing ones are stuck, I can't get it out I better get it out.

Anyways, what is the big difference between 6/8 and 7/9?

 

What kind and weight engine oil are you using?

 

6/8 will be better for lots of city driving ---- meaning stop & go traffic.

 

castrol 20w 50 only!!! and dont let anyone tell u different.
unless u live in very north canada or alaska, theres NO reason to run 10w30
info can be found in the fsm

i usually change my plugs every oil change, if not once in between. but im pretty hard on my
engine. racing it all the time.

as far as the 6's 7's 8's 9's are just going cold on up to a hotter plug.
one of those links i posted has that info in it

 

colder plugs (9+) ignite sooner and create a little more power because of that but they don't like a cold engine and start to run like crap.
hotter plugs (7-) like daily driving more and tend to last a little longer. they also have a little bit less constant ignition time, they vary by a couple milliseconds.

if your daily driving fallow the manufacturers spec and run 7's in the leading 9's in the trailing.

rod is right about the oil though.