purchased a 72 240z last owner apperantly had alot of work done to engine and then it sat for years. car starts and runs but not very well. checked compression and is very good on all cylinders, valve clearance is correct. pull of plug wires on 2,3,5,and makes no differance . changed wires and distibutor cap ect. timing is correct also. has triple mikunis stock fuel pump . changed front carb with back carb to see if would make diff. but didn't. any ideas what to do next. fuel pressure problem mabye? but cylinder 6 is strong ? help