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Discussion in 'Engine Topic' started by 72'z'steve, Sep 8, 2019.
Mine is the long yellow.
G72Zed,I'm really going to try the "780" because it is the original numbered carb it was born with,probably oversized for the grandpa driving I do,The 650 I have on has worked well but I need to go thru that one too from sitting,so I decided to see how the original will work!I never tuned a vac sec carb other than a q-jet always had DP's and my tuning is shade tree at best!!!I'll get the kit start with the long yellow [thanks Mark you come thru again!] and if it doesn't fall flat on its face and performs well I 'll play with it next year.I'll order the rest I need and play with it when I get back from the woods Monday-Thanks again both of "you'se guys" as we say on the southside here!!Later Steve!!
Quick Holley set up steps I put together yrs ago. My 1st Holley was in '74 when I owned a 1968 Z/28 while going to College.
Not over sized in my view, and if built and tuned right, one of the best and most versatile carbs Holley has made.
As you know GM used these "780" on all Z/28's from 67-69 302's and 70-72 350 LT1. If your intake is original, and does not have the divider cut down, your engine is only seeing 50% of the carbs air flow, and with the VS, it will only take what in needs, one of the reasons GM installed them on engines as small as the 302 Z's and as large as the HP 396/427/454 BBC's.
They worked very well. And Dual Plane intakes are less "carb CFM sensitive" compared to a single plenum, hence the reasoning for such a large CFM rating.
All my parts are here,all I need is the time to play with a straight mind,daily driver issues last 2 days,"new' caliper popped a seal on piston on tahoe,my Yukon trans cooler rotted out today,kinda sick of car stuff right now!! not the right state of mind to mess with the carb! needs to be fun not a chore!! I'll keep posted.All Camaro show this weekend,may take both wifeys 67 and my car haven't done a caravan like that in 15 years!!probably leave the 650 on until after-Later Steve!!
Well I felt ready for a challenge today,The masked carb rebuilder left his mark everywhere,scribed a "f" on the front fuel bowl[like you could mix it up] had bent the float arms down so you couldn't get adjustment-UUGGHH,I had spares so they got changed out.My vac sec cover was overtightened and didn't seal properly with the new diaphragm had to flatten out the sealing surface.he played with the secondary throttle blades to shaft,not perfect,but I couldn't loosen them up,know when to leave it alone.I'll put it on next week and play-it may go back on the shelf if its really dicked up-I'll keep posted Later Steve!!
You felt up for the challenge and gave it to someone to take apart and F it up. Nice. All you had to do was follow my web site instructions under Holley.
No Mark,The "masked rebuilder" I refer to was who ever did this foolishness 30+ years ago!!!Sorry I wasn't clear on that!! I had your page up today while I worked on it on the kitchen table [don't tell wifey] used it multiple times! I'm guessing there was more than one "masked carb rebuilder" over the years as I mentioned earlier someone had drilled the primary throttle blades,-someone else filled them in-I still like the "f" they scribed on the front float bowl,if you put it on the rear  the fuel line isn't there and  theres only one accl pump and its not where it belongs-OH well Later Steve!!
It all good! I appreciate all the help!,I hope to put it on next week and hopefully dial it in and it works fine! The title is after all "my poor factory holley carb" I believe I've done it better justice than the hacks before me-it deserves it!-Later Steve!!