Yuck. Moving Carp, IMO, is not a good move. He posted a .296 average and a .885 OPS last year. His 162 game average for counting stats was 17 HR, 82 RBI. As a bench player, that's an extremely valuable bat. Plus, we don't have any backup 1B other than people who are already in the starting lineup (Nava, Ortiz)
Keep Carp. If JBJ isn't ready yet, you can move Vic to CF, Nava to RF, and slide Gomes into LF. But regardless of that, it's not going to be a 2 week try out for JBJ. If he gets benched or sent back down, it won't be until Memorial Day, at which point you will have had some time to turn a deal for someone if need be. But don't get rid of Carp because a kid struggled coming out of AA and going straight to the MLB.
Player A AAA Stats: .288/.374/.409, 164 G
Player B AAA Stats: .275/.374/.469, 80 G
Player A Stats in 1st 31 Games of MLB (Age 22): .191/.258/.303
Player B Stats in 1st 37 Games of MLB (Age 23): .189/.280/.337
Player A is Pedroia. Player B is Bradley.
You need to learn to have patience when players struggle after getting called up. Every player has their lumps they have to go through. There's a reason that you look at a players minor league track record and his ability to adjust rather than just looking at numbers from 37 games of his initial year at the highest level of baseball, freaking out, and making a bad trade.