Это можно сделать с помощью функции Reduction от functools:
a = [(14, 2), (14, 2), (16, 2), (14, 2), (15, 2), (15, 2), (21, 2), (15, 2), (18, 2), (15, 2), (19, 2), (25, 2), (22, 2), (17, 2), (31, 2), (26, 2), (21, 2), (25, 2), (29, 2), (33, 2), (25, 2), (23, 2), (25, 2), (19, 2), (12, 2), (29, 2), (18, 2), (21, 2), (13, 2), (13, 2), (18, 2), (11, 2), (12, 2), (20, 2), (23, 2), (17, 2), (14, 2), (17, 2), (12, 2), (13, 2), (15, 2), (21, 2), (15, 2), (19, 2), (22, 2), (16, 2), (16, 2), (13, 2), (17, 2), (18, 2), (20, 2), (18, 2), (13, 2), (13, 2), (18, 2), (14, 2), (13, 2), (22, 2), (14, 2), (25, 2), (22, 2), (9, 2), (18, 2), (22, 2), (19, 2), (13, 2), (14, 2), (15, 2), (13, 2), (17, 2), (21, 2), (18, 2), (21, 2), (18, 2), (15, 2), (16, 2), (13, 2), (16, 2), (16, 2), (15, 2), (11, 2), (24, 2), (15, 2), (12, 2), (20, 2), (21, 2), (21, 2), (14, 2), (11, 2), (26, 2), (17, 2), (21, 2), (16, 2), (13, 2), (15, 2), (13, 2), (12, 2), (22, 2), (16, 2), (13, 2), (13, 2), (22, 2), (12, 2), (16, 2), (16, 2), (21, 2), (19, 2), (15, 2), (16, 2), (16, 2), (13, 2), (14, 2), (14, 2), (20, 2), (14, 2), (20, 2), (13, 2), (19, 2), (20, 2), (17, 2), (17, 2), (25, 2), (22, 2), (22, 2), (22, 2), (14, 2), (19, 2), (20, 2), (16, 2), (13, 2), (19, 2), (16, 2), (12, 2), (18, 2), (20, 2), (19, 2), (18, 2), (15, 2), (22, 2), (18, 2), (20, 2), (14, 2), (19, 2), (16, 2), (18, 2), (28, 2), (14, 2), (17, 2), (17, 2), (23, 2), (18, 2), (24, 2), (17, 2), (18, 2), (18, 2), (22, 2)]
from functools import reduce
b = list(reduce(lambda a,b:a+[[b]] if sum(a[-1])+b>50 else a[:-1]+[a[-1]+[b]],map(sum,a),[[]]))
print(b)
# [[16, 16, 18], [16, 17, 17], [23, 17], [20, 17], [21, 27], [24, 19], [33], [28], [23, 27], [31], [35], [27], [25], [27, 21], [14, 31], [20, 23], [15, 15, 20], [13, 14, 22], [25, 19], [16, 19, 14], [15, 17], [23, 17], [21, 24], [18, 18], [15, 19], [20, 22], [20, 15, 15], [20, 16], [15, 24], [16, 27], [24, 11], [20, 24], [21, 15], [16, 17, 15], [19, 23], [20, 23], [20, 17], [18, 15], [18, 18], [17, 13], [26, 17], [14, 22], [23, 23], [16, 13], [28, 19], [23, 18], [15, 17, 15], [14, 24], [18, 15, 15], [24, 14], [18, 18], [23, 21], [17, 18], [18, 15, 16], [16, 22], [16, 22], [15, 21], [22, 19], [19, 27], [24, 24], [24, 16], [21, 22], [18, 15], [21, 18], [14, 20], [22, 21], [20, 17], [24, 20], [22, 16], [21, 18], [20, 30], [16, 19], [19, 25], [20, 26], [19, 20], [20, 24]]