That's the tough part...the 260E has no provision for an EGR valve other than a untapped bung on its exhaust manifold. High NOx tends to indicate high combustion temperatures.

Because your other numbers look okay, ensure that you're running the highest possible fuel octane to ward off detonation (pre-ignition) and that it is as close as possible to 87C (thermostat opening temperature) when the test is conducted. Let us know how it goes...

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