Herbz, I had the same problem until I read a magazine article about gear changing. Upshifting, as soon as I release throttle I change up only letting revs drop slightly. Downshifting as said before quick blip of throttle normally does job.
I was letting revs drop off originally and started to think I had a gear box problem, took a bit of practice but ok now.
First gear smooth when cold, but once warmed up always clonks.
Apply slight pressure to gear shift so ready to change up.
All about timing.
good luck
Danny
TBA 04