[Formerly Steve Wilkinson]

I'm not sure I understand why you think "a rev limiter" is the problem. (I have two MSD 6ALs, twin ignition, and my rev limiters are set at 7,300 and 7,500 rpm, for what it's worth--big-bore short-stroke engine.)

Anyway, I don't think the MSD boxes _require_ a rev limiter of any sort to work--it's an add-on. If you don't add the rev limiters, the thing will just let you rev to infinity...well, probably somewhat sooner. Doubtless you have a bad box, but I don't think whether or not it has a rev-limiter chip is the problem.