Problem converting 73-1/2 CIS 2.4 to Webers, what distributor to use?

[CoreyJ]

I have a 1973-1/2 2.4 911 that's been converted to Webers. It idles great, and accellerates OK, but at a steady 3,000 rpm while driving it backfires through the carbs. This still has the original 73-1/2 CIS distributor that I have installed a Pertronix electronic ignitor in. My question is - is this distributor appropriate to use with carbs? Is the distributor's advance the same as one with carbs - I currently have the vaccum advance connected to an intake manifold on one set of the Webers. What should I use for timing, 5 degrees BTDC? one of my manuals shows different timing for the 72'-73' models with vaccum advance.

From the ignition side, I've switched out the distributor with another 73.5 CIS one I had with no change, and switched out the coil and Permatune without change. I've also cleaned out the float chambers in the Webers so I know they are clean.

Any help from someone that's done this conversion would be most appreciated!!