Just bought a 1966 GT coupe with 289 4bbl. Ran good for a few weeks and now having carburetor issues. Edlebrock Carb Model 1403. Will go from running great to really struggling. Restored very well by previous owner. Distributor looks good. No moisture, contacts good, timing good. Put new plugs in and cylinders 1,2,5,6 have heavy deposits on them after only a few miles of herky-jerky driving (really becomes an issue when giving it more than just very gentle throttle). The others remain clean. Any thoughts out there?