89 tII stock motor 20k on rebuild 10k on turbo. All i gotta say is check your plugs new ones made a huge difference. trailing on the left leading on the right. yes those are rx8 plugs

 

you maybe running a tad rich.

 

how many miles on the plugs?

 

mine looked like that also, just changed them the other day

 

ya its def running rich. i dont know why though 02 is new everything is in tip top shape ive only had the car since i wanna say aug sep of 2010 so not that long mabye about 10k miles ive put on it.

 

I would suggest using all rx7 plugs (stock are BUR9EQ and BUR7EQ) instead of using the RX8 plugs. I used to only change plugs out in my old nonturbo once a year, replacing the o2 sensor at the same time (roughly 40bucks total if using a generic bosch universal o2 sensor and the stock NGK plugs.) Never had plugs look that gnarly (the rx8 plugs on the right) in 5 years, and I used to beat the snot out of the engine (routinely redlined 1st through 3rd gear and generally cruised around 4k rpm's on long trips).

 

cuz your not driving a honda, your O2 sensor doesn't control your fuel at all unless your cruising.

i agree with firstrotaryexp, use the manufacturers recommended plug, the warmer plug will resist this ash build up a little better. mazda spent far more money on R&D then anyone else ever has or will.

 

mine were still worse

 

just an update on new plugs. gas milage is waaaaay better i was lucky if i got 200 miles out of a tank. i put the plugs in at 3/4ths full tank. now im inbetween a quarter and half tank and i just hit 200 miles. oh and i did but the stock fc ones all the way around got rid of the rx8 ones and im using trailings in all 4

 

Those plugs look pretty normal for a rotary plug with over 5,000 miles of use. Deposits aren't as bad as actual metal erosion...

 

yeah, I used to see 20~23 mpg in my nonturbo before I sold it. My first T2 avg'd 16mpg (had a bad coil pack i later learned). Always a good idea to replace the plugs and o2 sensor if you see average mileage starting to suffer, though I dont think ive ever replaced the wires in a single rx7 ive owned (on my 3rd set in my conquest as the turbo likes to cook my #4 wire )

 

I still have the original plug wires on mine. Perfectly fine after 20yrs.