i started messing with 6pak stuff in 1970. i was 22yrs old when i really got into this. i didn't have an A12 car; simply couldn't afford one. i bought new parts over the counter and my first foray into this was actually a dp6b. there were so many problems with them that guys actually took them off their A12 cars and put 4bbs on. there was no real info out there and if you could find something you were always at least 6 months behind because you had to wait for the info to come out in print. i believe it was in the middle of 1970 that car craft magazine did an article on 6paks. it was pretty comprehensive for the day. i use to save all that stuff but like a dummy gave it away. anyhow, it was the car craft article that showed us "shade tree" mechanics how to work the center car IAB. it explained the difference built into -1 carbs, deficiencies of the '69 carbs. i can't say i understood it all in 1970 but there's stuff i've never forgot. at that time i tried corvette carbs, 6pak mechanical, and factory carbs. by 1974 i had quit on it all, like most us in that era, and didn't pick it back up again until 1985. from 1985 until 2014 i was a die hard 6pak guy but have moved on since then. power isn't a problem with a 6pak; manufacturing errors (specifically edelbrock!) and emmissions are. get through those two and a 6pak is the best dual-purpose street performer.

i have to give credit to a member here, BSB67, for giving me a starting point on chasing the return orifice thing. i had a 6pak on my '65 coronet and always thought the power was a little lack luster. now this engine was never built to be a "real" performer but a good dual purpose street engine, i suspected some fuel delivery issues and BSB67 suggested tying a fuel pressure gauge to the windshield wiper and go hammer it! i did and what an eye opener. i was only getting 1.5-2lbs pressure at WOT with a 6903 pump. next came trying pump mods and juggling return orifice sizes but still keeping the pressure below 7lbs for street use. this helped a bunch. i never achieved 4+lbs at WOT but i did pick up about 1.5lbs and that was noticeable. fast forward to 2022, about 4 weeks ago, and i'm back into this again on a stock 440HP engine. this engine is in my '69 r/t and i decided to take the 272/.455 cam out and put the stock magnum cam in (cam swap was in june 2022 and i was chasing power brake issues). i put a new 6903 pump in it at the same time and gradually began to have some noise issues. thought the pump was the culprit, took it apart, did some fixing and re-installed (pump wasn't the noise issue ). car really ran crappy going down the road. did a fuel pressure check (which is what i should've done the first time) and now i'm cruising at 8lbs pressure and i knew that wouldn't work. you can build more pressure into a pump but i haven't figured out how to take pressure out of a pump. anyhow i took the .110" needle and seats out of the carb and installed .100", but i believe the real relief was opening the return orifice up to .053" vs the .031" i had been running. car drove beautifully. when the weather warms i'll do another pressure check but i believe i'm in that 6-6.5lb range now. the return does two things it's supposed to do, bleed vapors and control pressure. i have the original HP pump from my R/T and believe or not this thing still works! it'll do 8-9lbs at the pump but at the carb pressure will be noticeably reduced with .060" return orifice. a long rode of trial and error but i always learn something along the way.