I agree with Double D. The newer Eddie's don't have large enough passages to flow enough flow to match high air flow demands. When you have to jet down like that the carb is to small for the application.
I did some carb testing on the dyno a while back using a 11.8-1 426 wedge. I started with a 600 Eddy, I had to jet DOWN many sizes as it was Dead rich. Once I got it to 12.5-13.0 a/f and made a couple pulls you could tell the motor was struggling. Best pull with the 600 was 444hp and 386.1ftlbs. I installed a 750 Eddy and only had to drop one or two jet sizes and it made 463.8hp and 508.5 ftlbs. Going to a 850 double pumper the jetting was spot on.
There are a few issues with the Edelbrock/Federal Mogul AFBs. The restriction in the secondary booster's is discussed here:
Edelbrock 1407 booster discussion Speed TalkAlso the original 750 AFB Carter carbs have a different length booster which places it correctly just below the vena contracta. Edelbrock and Federal Mogul use the 625 carter booster in the 750 which is too short and delays the onset of primary booster flow.
The older Carters have a better sized and placed emulsion package. Easiest thing to do would be to find an old 750 carter and place the boosters in your Edelbrock carb.
Hope this helps
Hysteric
