120 sounds extremely large to me...
Did you do a plug chop, or did it run better with every larger size jet that you tried - did 118 really run better than 116 or so ?
Or do you just assume it's running lean because the exhaust is popping - which is more often caused by other problems, like a leaking exhaust gasket, failing air cut-off valve in the carb, or a failing cutoff valve in the secondary air system...
Jetting higher than necessary is just a waste of power...