I agree its adjustable but you shouldn't fiddle with them because they are set up on a tester and they are adjusted at that time. If someone messed around with them then that changes things but if one were off significantly you wouldn't be able to dial in your HC/CO and have the car run right. If you had one that was flowing more than the other 5 on the one bank you would end up running 5 cylinder lean to compensate and it wouldn't run right. Plug colour would be off as well. If you had one lean you would have 5 rich cylinders to cover up the lean one, plugs would reveal that again. I say don't touch them, they are adjustable in that they are used to calibrate the distributor but not for final setup.