I have had the displeasure of working on one of these. Would not run - new plug, disconnect kill switch, etc. Had good spark, but couldn't get it. I only spent 1 hr on it as my mate had bought it, run it 3 heat cycles at no then low load, flushed oil.
Took it camping and wouldn't start. Never started again, was replaced under warranty. That failed as well, demanded money back (might have been edisons or something like that) and went and bought a used Honda.
Baffled me for a while
More interesting to you will be my other mates experience. Ran fine, took it bush, they heard it sound weird 'farting' noise and it died altogether. Tried everything, no go.
Next day, they tore it down (they do motorcross so know their way around an engine) as they figured it had to be valve timing - and they were dead right.
Apparently it slipped a couple of teeth on the gears. So much that it didn't kick back.
My mate said the gears were made of some seriously 'chicken sh*t' grade metal with teeth that looked like they were cut by a 8th grade metal work student.
They got one more day out of it and it did it again.
Fixed it, and suddenly not making any power. Inverter spontaneously died
Last time he saw it it was sailing over the back fence (which is hard as they aren't that light)
My view on this is that (since they go straight to 3600 rpm) they don't bed in right on first start up. I have read that the hardness of cam lobes increases significantly after some effectively 'work hardening' over the first few heat cycles. Thats why people recommend zinc in run in oil.
Maybe the load on the soft teeth straight away gives enough wear clearance to slip
My main view is they are just made of bad metal
