IMO.....
Are the Carter/Edelbrock AVS2 carbs configured to open in progression, like the origional AFB's were? Front half of the rear carb for approximately 1/2 of the time with the front half of the front carb opening and the rear half of both the rear carb and the rear half of the front carb opening together (governed by in this case, the AVS's air valve blade spring tension). I concur with the others, the carbs appear to be too large or jetted too rich. I'm not sure that the primaries of both carbs can be leaned sufficiently to prevent the over rich condition noted, without some modifications
Remember that the Carter/Edelbrock carb design utilizes the primary booster venturii as the source for ALL the idle and off idle fuel transition circuits. The metering jets and rods DO NOT control the fuel during low speed operation but the fuel flow origionstes in the jet with the metering rod at its largest diameter when the step up piston is fully down. The primary boosters and venturii design are very efficient and are likely feeding too much fuel at lower RPM operation. The black plugs are not likely to blame but are the results of the excess fuel but are collateral result. You don't say what cam, engine vacuum, compression ratio or ignition system settings, all of which will effect spark plug coloration and overall performance. Running two AVS carbs in tandem, was IMO, ill advised, but since they're bought and paid for, we'll have to figure out how to "fix" the issues. Do you have any info on the carbs innitial jetting....INCLUDING primary booster fuel feed restrictions, air bleed orifice sizes and any primary throttle plate closing angle dimensions (opposite the idle fuel transition slot), as this affects when the transaction starts to feed fuel. These primary booster venturii fuel feed circuits are thru drilled orifices and are not readily change-able except by drilling, but making them smaller is extremely difficult. Just talking out loud about possibilities......
BOB RENTON
