Jaguar Repair: Failed Smog Nox test, vanden plas, 1985 jaguar xj6

Question
1985 Jaguar XJ6 Vanden Plas 4.2 litre failed smog for very high Nox reading. Max 742 @ 1525 rpm, my reading 1907. Is there an adjustment I can make to correct what is probably a lean air mixture?

Thanks

Answer
Hi Martin,
NOX is the product of burning of the Nitrogen in the air in the combustion chamber when the combustion is too hot. This can be caused by a lean mixture, incorrect ignition timing or even engine over heating.

If the engine has not shown signs of over heating, you should check ignition timing and then check the CO in the test results to see if it shows lean.

Howard