Because with those big 48mm carbs the fuel atomizes better when you heat the carbs a bit, also if you look at the diagram of the cooling system you will see that coolant only flows through them when the thermostat is closed. As it opens the coolant is bypassed from the carbs. So they never really get that hot unlike an automotive system.

 

gotcha, thanks for the info. makes perfect sense now

 

VTR on the right, RC51 on the left.
On run 2 I put down 108.6 hp. w/ just Jardine slip-ons.