I've been having  a problem with the mixture balance between rotors changing as RPM increases on my 13B from day 1 with my install.  In my case I had installed the MAP connection in a convenient hole on the primary runner for rotor #1 of the stock 6 port lower intake manifold.  I wrongly assumed the response time of the MAP sensor would be slow enough to damp the pulses in the intake but obviously this is not the case.  Moving the MAP connection to be just after the throttle body completely resolved the problem.

Perry Casson   Glastar/13B - 20 hours
http://eaa154.dhs.org/perry