There is nothing wrong with your CDI-units ... the quality of your points and distributor condition is suspect, though! And the carbs contribute to popping and backfiring, too!
Read this thread about distributors ... and consider removing your dist. at TDC #1 ... and doing a partial disassembly (the drive gear doesn't need to come off unless play and wear of bushings or fiber washers (endplay shouldn't be more than 0.1 mm) is evident!
distributor lube...