Looking through the Merc Parts listing many of the TB-IV igntion Modules are listed as "with rev limiter". Is this and external Rev Limiter fed by a wire or does the module have the rev limit function built in? I am using an old V8-24 Module from a pile of parts circa 88 or 89 and I seem to stop building RPM right at 47 or 4800. The module I am using may be the stock one from parts pile or could have been replaced somewhere along the line. I thought I may be hitting a rev limit.

Anyone know how the rev limt works on TB-IV or if there really is one?

I was told there is no rev limiter built into the TB-IV module

There is no revlimiter in the Thunderbolt IV module, although the carbureted HP500 did have an external revlimiter box wired into the T-IV.

Sounds like you've got other problems. Tired valve springs make a very effective rev limiter.

Good luck,

Kurt