I've left my car idling twice now, once for 45 mins (got stuck inside work), and once for about 15 minutes (took too long to run into the house) and both times I came out and my plugs had fouled up.

The 45 minute time I came out and it was only running on one rotor, so I had to pull the plugs and clean them off, the second time it cleared up after some revving.

I'm running NGK Copper 9's all around. Anyone else had this happend to them? I was wondering if this was normal when running the colder plugs on the leading.

Please don't critisize me for letting it idle that long, its only because my starter is crapping out and its easier to let it idle then to have to try and start it if i'm just running in somewhere.

 

holy crap, you let your car idle outside for that long? and nobody took it? wow

you know, you can pushstart your car fairly easily if your starter is going, just park it going down hill, its even easier like that...

 

Yes, I've had this problem before when my a/f was tuned REALLY rich during idle. I now run 13.0~ a/f at idle and NEVER have fouling plug problems.

 

Yes, your car is running rich. Replace the plugs and find out why your car is running so rich and you will solve the problem.

 

Mazda install two different heat range plugs in the rotary engine for a valid reason. Millions of dollars testing prove this.

This part I am unsure of the technical reason for..............At around idle speeds to about 2000rpm, your leading plugs do most of the work. Above that your trailing plugs take priority.

If you are using your FD (92-02) RX-7 on the street then you should be running the following plugs for best results.

Leading........... BUR7EQ
Trailing............ BUR9EQ

You can use the Platinums too if you want to get better plug life.

The reason for the different heat range plugs is due to the pressure difference between the leading & trailing plug holes. There is a greater pressure above the minor axis (trailing port) than below it (leading port). This is why the plug port is far smaller than the leading one.

The reason why many people (wrongly) believe that 9's all round work well is that the 9's in the leading help reduce the chance of ping. True, but not for the right reasons plus they do increase fouling as they are too cold for the leading position in a street driven car.

Your trailing plug has a higher chance of after glow on boost at 6000rpm than the leading does so if you want to go up 2 heat ranges in the leading, you should be doing the trailing too.

I know that there are a dozen different points of view on this subject but think about it this way.

If its good enough for Mazda, shouldn't it be good enough for you too.......???

 

Good write up. However, some of us have used 9's all around with good results. I myself have, within the last year, bought 4 SETS of plugs. I USED to change plugs every month, but that all changed when I purchased my wideband and tuned the driving range for 13 a/f.