So You say low "starter-rpm" was the problem?
Yep, at least it solved my case. I almost went mad when the engine didn't fire up. After 1/2 hour rechecking everything without any result, I put 24V on the starter for the last try... it started up immediately. I was happy, my neighbors not...
I use the std spark gap (approx. 0.7mm)
Saludos Ole