So ECU variable timing manages the detonation (thanks for clarification) - getting round low octane at any alt I guess.
And efi with lambda ought to manage the mixture as air pressure varies.
> EFI with an air pressure sensor (throttle position and temperature sensor) manages the mixture alongside which the lambda sensor provides the feedback on the EFI's chosen mixture. The lambda sensor is not critical for mixture regulation (open loop systems don't use the sensor, closed systems do).

Richer (with cooler running benefits) may not be relevant I now realise, if the best efi/lambda manages to always make a perfect mixture.
Or at 4000m+ can efi only be expected to be a lot better than a carb, but still richer than optimal?
>Firstly, "richer" is a relative term that represents a compromise over the optimum stoichiometric mixture to achieve a particular drivability/performance aim and cooler relates to the environment of the cylinder where combustion is taking place not the engine as a whole. There isn't some intrinsic flaw with carbs and altitude. It's the transition between different altitudes without mechanical intervention that makes FI so appropriate and convenient.

Q - Will a modern bike run better at high altitude? ..........
A - ... so the modern bike will run better at low altitude
So that's a no, or did you mean high alt?
> I thought that was obvious, if the modern bike runs better (power etc) at low altitude on poor octane fuel then it can't be better at high altitude.

Thermodynamics was never one of my strengths but where motorcycles are concerned it is fascinating.

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