Hmmm, I have long been aware of carbon deposits being the cause of pre ignition but to suggest that these come as a result of dilution of the oil by petrol is a bit far fetched. Such severe dilution would, I feel, bring about other serious problems as regards early engine failure to say nothing of the possibility of crankcase detonation!
A graph showing the spark occurring after top dead centre is worrying too.
I am not sure why low revs are seen to be the cause of all this, perhaps I am just a bit old fashioned?
