[Maddog]

I feel your pain, I was the lead mechanic charged with keeping 15 of those bastards running. We used them every day 365 days a year. The starting system is certainly its weak point. You need a good starter, a great battery and an understanding of its needs.
There is a friction/ idler gear that must be modified. This gear will slip upon backfire to save the case from damage. You must ensure the friction/idler gear is not slipping prematurely. If it slips then the engine will not turn fast enough and makes a wheezing sound. That's the compression release, too late to ease compression and causing a slow cranking speed/ no start condition.
Most Important ! If it doesn't start in the first 10 seconds of cranking STOP !
Key off wait 20sec. Try again. Still no start? Key off 20 sec. Now key on Wide Open Throttle and crank 10 sec.
Use this mix till you find the method for your machine. Never crank longer than 10 sec, I've rarely seen long cranking sessions do anything but flood engines.
It's a pain to remove the plug, but 90% of the time it fails to start its flooded.
Wish you were closer cause it's a knack to learning how to start these bikes. Out of 12 mechanics only 2 of us were able it (read) these bikes well.