The DCOE, IDF and IDA carbs are a marvel of engineering and quite simple but to operate correctly they rely on the basics being right.
If the carbs were sync'd on a Pinto and you then refit them on your Xflow manifold you will need to re-do them. It sounds like the front throttle plates are slightly more open than the rear, or, possibly but less likely, an air leak.
Ignition timing issues will not cause what you describe.
I have 'tinkered' with them with them for over 50 years on race and road cars both professionally and privately, I currently have a pair of IDF down draughts on my 1700 xflow 4/4. Let me know how you get on.
