Hmm. Well I would call that a little lean. The proper test is to run it wide open for a decent stretch, shut it down and coast to a stop. This gives the plug reading at maximum power without any idling etc etc.

If you are doing this then maybe enrich the mix a bit and see how that goes. You might find that you need to build a progressive throttle set up to keep it rich enough wide open without fouling plugs at idle. If you run out of reasonable adjustment room then maybe changing heat range is an option. Maybe one step colder if you have raised the compression with a different head or lots of machine work or both.

-Jesse

Ok, I can do that test. It seems good at high RPMs though.

If nothing else adjusting it a little more rich would probably be a good idea even if it runs fine. If that is what the plug looks like for all around driving then it could be getting pretty lean on the higher end. Tuning for performance is always a balance. Carl probably knows a lot more about this topic than I would.

You wouldn't be running a lead additive by chance?

-Jesse

Just wondering, lead would cause a buildup on plugs after a while if you were dumping a lot in the tank.