FC Race Car won't rev past 6000rpm under load
 

The car:

1986 RX7 NA, Aggressive Bridgeport, Weber Carb, FB ignition system, 285hp at flywheel. Running VP Racing M105L fuel (leaded).


The problem:

Took it to the track on the weekend, and sitting in the pits, it would rev right up to 8000 (and beyond if we let it).

When we took it on the track, under load, when it reached between 6000-6500 rpm, it sounded like it hit a rev limiter, but we're running stock FB ignition (coils and distributor) and there is no limiter, and it's supposed to rev to 8500.

Pull the plugs and they're BLACK! So either a) too much fuel, b) not enough spark. Jetting in the carb is correct for the application.

Any theories?