Trail Tech has a cylinder head temp gauge with a sensor that goes on the spark plug for about $40.
I also had a TU250X, it was a great little bike. I had a CHT gauge installed on that too.
On every scooter I've owned (quite a few) I drill a half circle of holes in the CVT cover just behind the clutch.
It makes a big difference keeping the temps lower which greatly increases belt life and reliability.
