I do hear valve chatter and pin pointed to the #6 but the thud doesn't change that i know of.
The thud is when i rev it and it comes back to an idle maybe half a second to a second after. and I can only make it repeat if I rev it up again. It is not repetitive with rpms. Plugs look clean, maybe running a bit on the lean side. But maybe the plug is fowled and I cant tell...
