Scooterotica

Sorry….. completely distracted by Red Ghost’s avatar of a moment.

The basic indicators are humidity and barometric pressure. As I understand it, hot weather and rain are symptoms of these not necessarily the cause. Jetting for road bikes needs to accommodate for the variability in those conditions. You won’t recognise the difference with a modern car because electronic fuel injection will measure and adjust the fuel load accordingly.
The basic rule I use is that if the engine is hard to kick over then compression is too high for road use IMO. In setting the dimensions for the heads on the GT kits I measured the trapped compression ratios (sometimes called corrected ratio) on about 15 good reliable engines I knew and had access too. This was done by removing the head, measuring the port, deck heights and gaskets then pipetting out the head volume (same way they measure heads in kart classes). I settled on a ratio based on these measurements and I think this approach, combined with others, goes some way to producing the reliability/performance that GT kits are known for.

I run an egt and i must admit the readings will go a bit higher on a cool day as the air is thinner, so to speak ,as it is running leaner. On a hot day the temps will go down a bit as the bike is running richer.
However, i have read that a really low egt reading (unusually low) and a high head temp reading can be an indicator of an engine that is blowing itself to bits as the heat is being retained in the piston and head rather than being dissapaited.
As Rich T said, the trick is to jet a road bike to compensate for weather changes.
In my opinion, it is harder to jet the mid range for cruising than the main jet for full throttle thrashing and if you run an egt you will see that the temps are far more likely to spike in the mid range at say 60mph.