Yes, should be closer to 11. Below 11.5.

Karlos's suggestion was a very sensible one. Retard the timing to see if that helps. However this will also reduce cylinder pressure which may hide a spark plug related issues. What is your plug gap?

When the noise happens does the engine misfire violently? If not then I suspect you are hearing detonation. For you to hear it at all with no det cans means its fairly severe.

Lean plus possibly too much advance is a recipe for detonation. Buy some det cans!



Rob,