Oh yes... the octane. It seems here in the States, we have Regular - 87 octane, Mid - 89 octane, and Hi - 92 octane. I wish I could find the 97 octane. That may be the culprit. I have a new tank of the hi in it, and hope it fixes the run-on dieseling.
I'll have to learn what the Advance/Retard is on the distributor and find out what proper heat range plugs to use.
Thanks