I'd say it was all about air density.
Colder air is MORE dense.
In order to maintain a similar air-fuel ratio, the denser air requires more fuel.
This is what the 'air density' sensor on the carb measures.
Denser air = more fuel.
On a similar but different note, the 'leaner' a fuel mixture (to a point), the better the burn therefore the more power can be had with better fuel economy, hence mhy ECU tuning is important. The 'stock' tune is often richer than a tune that will deliver max power, in order to allow for variation and to prolong engine parts.
DrP
