I have a 6 month old Kawasaki W800 I bought new. Sometimes when I ride gear changes seem stiff and clunky. Other times they seem smooth and normal.
Would anyone know what could be causing this? Doesnt seem to matter if the engine is warm or not.
As the motor cycle is 6 months from new I would recommend putting it into the suppliers repair shop under warranty. If you were to attempt any sort of dismantling to effect a repair you will more or less invalidate any warranties for the motor cycle.
The symptoms point to either a clutch or gearbox fault.
I know I'm a bit late to the party, and perhaps you are perfectly aware of the following, but I noticed that nobody has mentioned this: do you apply a bit of pressure on the shifter pedal, right before depressing the clutch?
Doing so helps to tremendously smooth out gear changes on many motorcycles, as the new gear is essentially spun up to speed before attempting to actually engage it. You'll find that the motorcycle will pop into the next gear much more willingly than when you just hit the clutch and kick up. Half a second of light pressure is usually enough - don't apply much pressure for a long time, as doing so will cause extra gearbox wear.
Some bikes are very sensitive to this technique, while others show no real improvement - YMMV.
You can even try clutchless upshifting, where you just apply upwards pressure on the gear selector and flick the throttle towards the closed position briefly. By reducing the throttle, you remove engine torque from the gearbox and allow it to shift (which you normally do using the clutch). If done smoothly and correctly, a clutchless upshift reduces clutch wear (since you're not using it!) and yields no extra gearbox wear. The chief benefits are a much quicker shift and less hand strain on long rides.
Note: personally, I don't recommend using a clutchless technique for regular everyday downshifting. When shifting down, good riding practice is to use the clutch in order to roughly rev-match the engine speed to the road speed. If you don't rev-match, the rotation speed difference is absorbed by the bike's inertia. This sharp and sudden engine braking effect can cause your rear wheel to lose grip and induces extra wear on the transmission and final drive. Nonetheless, as mentioned by DucatiKiller in the comments below, it's definitely possible to mitigate this effect and smoothen the shift to some extent by blipping the throttle open.
It's a Kawasaki, I've ridden two before and they both had fairly clunky gearboxes (especially between gears 1 and 2), it's quirky!