Yes I to have had the problem - it took 2 years and just under $3000 to find. Same problem easy to kick start , plenty of spark , starter turns over well.
If you put a multi meter on the plug capand give it a kick the voltage will be spot on - push the starter button and the voltage just wont quite be enough even though the starter motor is spinning at the right speed.
The answer to the problem is the starter motor free wheel bearing part no. 250 245-01 .This is meant to free wheel when the motor is running and engage when the starter motor spins.What I found with mine was that the bearing was slightly slipping when turning the motor over and with the motor running binding up and spinning the starter motor all the time.
Even though the bearing was poked it still felt alright to spin and turn aound and would grab like normal when spun by hand but under load in the motor it wouldnt work.
To try to fix this problem I'f fitted a new decompressor to the end of the cam , had sparks rewind the stator asy, fitted a new keihien carb ,bigger batteries and done all the updates as mentioned on this web site.
Since doing this the bike starts first push on the button hot or cold no problem at all.
Relpace this bearing before fiddling aroung with the carb ( it only costs $42) - If the bike starts 1-3 kicks with the kick start carburation is not the problem.
Hope this helps - good luck