Do not ignore a dodgy batch of fuel. I've had it happen to mine in a similar situation and detailed on another thread, this was about a month ago. I chucked in extra fuel (simple on mine, just file the carb needle) and it was still there, i cant do the timing on mine because it's ECU controlled and the only thing that stopped it at the time was a dose of Millers octance booster. As you say it hasnt happened since, i would be looking at a one off situation. As you know what det sounds like you will be able to back off if it ever happens again. Wonder if anyone has ever claimed against a fuel company for detonation induced engine failure caused by their fuel being off... ???