One thing to check on the DCOF is the pressed-in venturi. The carb bores can get a little out of round and the venturis can get loose. Using a needle-nose pliers, grab the venturi and see if you can pull it straight out (be careful of the choke plates; these and the shaft have to come out if the venturis are loose). If it comes out, or wobbles a bit, this is your problem. The only solution I know is to get the venturi out, clean everything real well, then use crankshaft bearing shim stock to shim the blank side of the venturi. It only takes a few thousandths thick stock. I remember (now this is 40 years ago) snipping a feeler gauge down to try and measure the clearance. Once I got close, I cut a slightly thicker shim out of the shim stock that would just fit inside the slot for the venturi (the blank side, not the fuel side). Then, put the carb on the bench so the bores are pointing up, put the shim into position. I left the shim a little long so a tiny piece of masking tape could be used to help hold it in place. The I careful pushed the venturi into position, then tapped it into place using a piece of soft wood as a dowel and a hammer to carefully tap the venturi in. Make sure the shim does not slide and bunch up at the bottom. Once the venturi is secure, take a razor and cut off the excess shim stock. The repair will last the life of the carb. I've used this on other carbs like the Weber/Holley 3100 that came on the Chevy Vega. Seems all the diecast carbs warp over time. Back in high school, my sister had a red 1100R that she named Rubella (it had the Solex carb), and I had a '61 1200 Cabriolet that I transplanted the 1100R engine with a Weber, and the front disc brakes from the 1100R. I used to know every wrecking yard that had Fiat 1100/1200s in the Portland, Oregon area.
