When I kickstart my B40 I find that a number of the kicks don't seem to be moving the piston. It feels as though there is some sort of 'tension' as its not the same as kicking with the clutch level pulled, but it doesn't sound like there is any spark or ignition etc. After doing this approx 6 or 7 times it suddenly wakes up and the engine comes to life and starts pretty easily. Im wondering if this is something related to clutch plates, or am I barking up the wrong tree?)
Not sure exactly what you mean?
When kicking it over with the clutch pulled in, there should be virtually no resistance ( just the gearbox mainshaft and clutch assembly rotating through the oil). With the clutch out, the primary drive is engaged and the engine should turn over, unless the clutch is slipping very badly. I believe the correct way to start a B40 is to pull in the decompression lever and gently kick the engine just over TDC, then release the decompression lever and swing through with the kick start to turn the engine over. Supposed to not put so much strain on the kick start mechanism.
Sounds like clutch slipping.
Yes Im pretty sure its a slipping clutch, although the clutch works well when riding.