Pull the head off and wipe the inside of the liner with a clean rag to check for peeling of the nickel plating. If you can see any brass whee nickel once was then that might explain your problems. If it doesn't then perhaps your needle is changing in flight at certain rpm/vibration levels - check to see that the spring steel clip has plenty of pressure on the nedle valve and clicks with authority.

If one click is solving your problems then I think you still might be too lean. Richen it up 3-4 clcks at least.