Hi there and welcome back!
As to chasing your problem to me it sounds like an ignition issue, but could also be fuel related.
The best way to rule out the ignition would be as soon as the machine cuts out immediately check for spark, if it is weak or non existant you know something is up there, it may be either the coil or rhe ignition module (more likely the ignition module if it is an older style one).
As for the O rings causing the hassles I would surely doubt it, they generally cause hard starting and engine running rough/ overrevving.
Cheers Joe.
