'73S engine surging

My 2.4S has always had this surging problem between 2800-3200 rpm under a light load. Typically driving around town in 3rd gear. The motor accelerates fine from idle to redline. A friend with another '73 S experiences the same thing. Is this typical of these motors?
The motor, mfi and throttle bodies have all been rebuilt. When JW set the motor up they plugged the distributor vacuum line, and the motor is set up to run a few degrees advanced at idle.
My mechanic has adjusted the mfi a few times. The surging is still there, sometimes less, sometimes more.
Any suggestions on what else to try?
'73 S coupe

You're in Seattle? You might give ROTHSPORT down in Tualatin, OR a ring. Gordon Ledbetter there really knows MFI. The downside? You might have to wait until after race season to get in...

Chris' German Auto in Bellevue would be another strong candidate.
However, I am with Paul. If you can hook up with Professor Ledbetter, the problem will be solved in a very timely fashion!

Used to be in Seattle, now in San Francisco Bay Area.

I have the guy for you.
Peter Sorensen @ Porsche Restoration in Crockett, CA.
(510)-787-2200.