As soon as I can confirm what our problem with this engine is I plan to do something with the carb. I'm thinking that the BG carb is just way too rich for this engine. I'm thinking it is the metering blocks not jetting or PV. The off idle stumble/ flutter happens in park at 1,000 rpm and continues to about 1,800 rpm however when I drive the car and from a stand still nail the peddle to the floor the car stumbles and flutters all the way down the road until I let off the peddle and then it stalls out dead and is hard to restart! I pulled the plugs and one looks heavy carbon on it. All look black sooty at base, 4 have slight dark tan on the center and electrode, and 2 are slightly wet. These NGK plugs have 100 miles on them and they look like they have 10,000 miles of running rich on them. We are using a friends Holley 750 right now. We would like to stay with a double pumper carb for tune ability! When they say a plug has carbon build up, what causes that???