Hot #4

Greetings,
I just picked up a '78 650 SR and did the usual carb cleaning to get it running, it fires up nicely(though number 4 header doesn't reacch the heat of the others while idling), and has nice snap until it's warmed up, then a pronounced low end stutter. After a 5 minute ride, Ipulled the plugs and 1-3 are sooty, while the electrode on 4 was white, soit's hot. #4 carb had half the raised area on the screwdriver slot on the mainjet broken off, also the brass tube sticking down from the carb body into the float bowl(enricher circuit, I think) is snapped off. #4 is my main concern. Am I looking at an intake leak, or maybe some boob lowered the mainjet needle?
By cleaning, I mean I scraped the varnish out of the bowls, removed and cleaned all jets an tubes but I haven't soaked the bodies yet.
Anyone?