[wacio]

Replace oil and check air cleaner. Let oil out of air box. Checking for loose fasteners is good idea too.

Also the big bore kit is just a waste of time. This bike is never going to be fast - and not intended to. It may become much less reliable though. One of the weak points of GZ250 is head - seizing valve stems and dropping seats are common already - and may get much worse if pushed hard.

Keep it below 60mph and it will last. Going past that is something this engine hates.