That hard fuel line kit should be ILLEGAL to sell. Yeah, lets put hard lines on an engine that grows maybe 1/4" and then shrinks when it cools. Can you say metal fatigue? Eventually, those lines are going to crack. When that happens, I don't want to be around.
That kit could be fixed with a 2" long flexible hose between the carbs.
I just worked on an engine that has that setup and told hi, to get rid of it or modify it.
@TRP bring the carb with both barrels reading 3 up a touch with the idle speed screw on that carb. On the carb that reads 3 and 4, bring the low barrel up with the idle air bypass. Then re-balance and make it happy at idle with all 4 throats the same at whatever idle speed you prefer. Don't shoot for any particular reading, just all 4 the same. Then do a high speed sync.