Rejetting - A few quick questions.....

It's not so much a case of time, but rather of use.

The cleaner your engine is, and the cleaner and more temperature stable it
runs, the better. It's not a case of just gap though, it's MUCH more to do
with the condition of the ceramic insulator. Once that starts to go, you
don't get as clean a spark, and then it's all downhill from there. For
something that seems relatively simple, spark plugs are decidedly
complicated bits of kit.

 

With a good ignition system, ie nice high voltage etc, you can replace the
standard plugs every 6000km if you're keen, or let them go till 12,000km. At
a few bucks each (cost be about $22 a set or so) it's not much to baulk at.
I always liked to replace them every 6000km just to be on top of it all.

Cam
'03 954 (but I think now I've got those friggen fancy iridium ones .. meh)