rejeted carbs, now backfire at 3k

[davemccorkle]

I have a 2.7 RS with IDTP webers. They were setup for a 2.0 engine so I rejeted them as follows.

main 145
idle 60
air corrector 180
emulsion tubes F3

After setting them up I still seem to have backfiring mostly on deceleration around 3000. It runs fantastic but just backfired through the exhaust around 3k. The engine has on 2000 miles on it and everything is either new are rebuilt. I guess the intermediate circuit needs a change but not sure what. Any thought from the experts. I have work a lot with Paul Abbot and he is fantastic by the way. I have all the tools, and the color tune is awesome but I just cannot get this 3k backfire thing fixed.

[davemccorkle]

Sorry for my horrible typing skills by the way.

I also changed the Venturis to 34mm

[davemccorkle]

problem solved already! there are two vacuum ports below the right hand carburetor. cylinders 4 & 6, not sure what they are for or what they go to but once i plugged them up everything works perfect. Can someone tell me what those ports may be for?

[R_Builder]

One usage for them is for the vacuum advance on the distributor...