2F dieseling at shut off.

May 6, 2020
There are many reasons for dieseling. What do the plugs look like? Are they showing sign of getting excessively hot? When you turn the engine off an fuel air mixture could be ignited by a hot plug. You mention the timing bb is at the bottom of the window which I believe indicates the timing is advanced past spec. Typically dieseling is from hot spots in the cylder. Carbon build up can increase the compression ratio, advanced timing creates more heat. then running lower octane fuel, will all contribute to the issue. Does this engine ever see faster speeds or higher rpms for any length of time? Maybe a different heat range plug might help too. Sometimes a good flogging can blow the carbon off the top of the pistons too, but that's up to you.

When I was wrenching and someone brought in a older carb'd vehicle that was running rough and we suspected carbon buildup, we'd tell them to go out and try to get it up over 100mph then come back if there's still an issue haha. Give a good flogging like you said. It really does help.

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