You are doing good work here Sasquat. Keep it up until it reaches a solid conclusion.

It is possible that it takes more than one cause occuring simultaneously to set up a nailing condition such as the intermittent type at low throttle. Revisit your theories with this in mind and see if you get further.

If you would not mind could you please redo the list you started after you get all of the input and try to prioritize it and organize it. You might also add valve adjustment as a potential contributing cause.

This nailing is an insidious condition that can do damage over a long period of time.

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Dionysius