It wasn't leaking there, but I read somewhere that the hot rodders used to shove wads of aluminum foil into the small ports beneath the carb. So I rolled up a piece, and blocked the straight passage under the carb. It seems to warm up normally, and no more bucking. Even in overdrive.
It's not a proper fix, but it's going to get me better mileage, and it's a great feeling having corrected this after dealing with it for so long.
Thanks for the advice guys!
