I have now run in my bike and still find it running a little hot. The fan is on most of the time. Is this normal? I remember soemone Perce possibly telling me to change the jets from stock to something else but can remember the numbers. Can anyone help?

The bike is also very sharp which I thought I'd get used to and would soften with time but now I want to soften it myself. How do you retard the ignition on these bikes and are fly wheel weights available and worth adding?

Try going one richer on the pilot jet (slow jet). I'm pretty sure the stock one is a #35. Try a #36 or #38. This will also have the effect of slightly softening the power right off the bottom.

As for the timing, you need to remove the pickup and elongate the screw holes to move it. You can only get a couple of degrees, but ever little bit helps.

The other option is to install the thicker base gaskets that are available from GasGas. This will lower compression and soften things too.

I've just recently tried a Keihin carb on my 280. It seems slightly softer on the bottom, but revs out MUCH farther...way farther than I need for sure. I was disappointed in it at first, but after a little tweaking on the jetting it seems to be getting better and I'm reasonably happy with it at this stage, although I'm not sure I'd recommended on a "cost vs return" basis.