23/09/2026
Have you seen the ignition timing Field Note on the site? If your car has stock engine management there is a small amount of power the factory left on the table, and the same job fixes a lot of cars that idle badly.
The factory base is 10 degrees before top dead centre. That base is the fixed reference the whole curve is built on, so if it is wrong the whole curve is wrong, and it moves without anyone noticing: change or adjust anything near the sensor and the timing shifts.
Setting it needs a 12mm spanner, a timing light and a paint pen to highlight the notch on the crank pulley. In the diagnostic box, bridge TEN to GND and the ECU holds a fixed 10 degrees with the curve taken out of the picture. Warm, no electrical load, base idle around 850 rpm. Then read the mark under the strobe. On a Mk1 you slacken the slotted sensor at the back of the head and rotate it to bring the mark to 10, then lock it down and read it again, because tightening it can nudge the timing. On a Mk2 and Mk2.5 there is nothing to adjust. The trigger plate is fixed from the factory, so what you are doing there is checking it fires at 10 degrees and setting the base idle.
For a lot of cars with a tick of rough running or a slightly off idle, that alone is the fix.
Then the free power. Petrol in the 1990s was not as good as it is now, so the factory left the timing soft to keep a margin against knock. We advance the base from 10 to 14 degrees. Each notch on the pulley is 2 degrees, so on a Mk1 that is two notches. A stock Mk2 or Mk2.5 cannot have its ignition timing changed at all, the factory plate is fixed, so there the mod means fitting an adjustable timing plate first.
The VVT is the one engine that does not get this mod at all. The cam sensor does not like it, so leave a VVT car at 10.
Where it bites: this is free power, not a free lunch. Once advanced, run 99 and keep it in the car. A Mk1 has no real knock protection and the Mk2 knock sensor is basic, so your own ears are the safety system. Pinking or rattling under load, especially hot or pulling up a hill, means back it off. If in doubt, set it back to 10. Standard is never wrong.
The write-up, with the diagnostic box maps and every figure:
https://fojiraceworks.co.uk/field-notes/mx5-ignition-timing/
If you would rather we set it and check it on the light:
https://fojiraceworks.co.uk/contact/?job=engine
