Going back over the thread....

The "white smoke" was more than likely unburnt fuel/ water vapour.

The rattly exup is just in need of a slight tension on the opening cable to prevent the valve rattling on the stop in the chamber.

These bikes aren't known for cam chain wear until high mileage is attained.
The tensioner could be between the teeth on the ratchet but that will not prevent smooth running and after slightly more use will drop into the next position and quieten down..

What did you do to weaken the rich running you encountered initially.?

As Dobbsic says....unburnt fuel igniting in the silencer.....nothing out of the ordinary when attempting to start a reluctant engine.

The coolant ?

That looks like plain water without additive but carrying suspended rust particles.
Reverse flush and refill.
I would run antifreeze on a track bike.
It is only for racing that it is prohibited.
Antifreeze; or as its name implies...anti corrosion additive....does what it says on the tin.!