GY6 trivia

[axy]

"The cooling system is in part crippled by the internal routing of the timing chain; nearly a quarter of the cylinder bore receives no direct cooling. Aftermarket "big bore" cylinder and piston kits are available to increase the displacement as high as 180 cc, but engine temperature must be carefully monitored and full-throttle operation limited, to avoid overheating and engine failure."

[Cortez]

Monitor the temperature? My ass.
It's probably cheaper to put a fan in there then run wires for a temperature readout.

[axy]

I believe that our climate in 99 % of cases is not an issue for cooling.
Perhaps a few days in the summer during temperature peaks when it is 35-38 C.

Even during those days, I have noticed that on Beverly the fan turned on maybe a few times in 4 years, and it was only while driving two up.
I am not sure I ever heard fan running on P250S. Who knows is it functioning properly at all.
This includes driving on the highway two up in the middle of the summer flat out at top speed for 600 kms.

This might be bigger problem for countries in the Middle East/in equatorial belt.

Back to A125 and cooling, I have many times noticed power drop on overheating liquid cooled Piaggio engines, and even saw the temp gauge needle redlining, but never noticed anything like that with A125, Yamaha, People, Bev, Kawasaki...

However, this is an interesting observation. Obviously, engineers had to put a lot of mechanics in a small package and 1/4 of the engine casing being not-cooled is a consequence. These issues are present in other areas too: for example, in boxer engines, outer cylinders are usually much better cooled then inside ones. This can also cause issues.