I recently had my motor completely rebuilt, After assembling the bike I got it
running near tip top, the only change from stock is filter pods and upping the
main jet to 105. I was getting a good tan color from the plugs and went on some
short rides.

Running along at highway speed (about 8k) for less than a couple minutes I lost
the left cylinder, the right would fire but the left made a scratching noise
which led me to figure there was mechanical failure.

After tearing apart the motor the cylinder walls looks amazing as do the pistons
and rings. All the valves are black except for one which is tan. What are your
thought?