You fool, a 950 Holley is too big

Discussion in 'Holley' started by sporty-to-GN, Jan 4, 2018.

  1. sean Buick 76

    sean Buick 76 Buick Nut Staff Member

    Get the model number off the carb...
  2. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    I'm curious about this because about 10 years ago I restored a `70 GSX, Stage 1, 4 speed with factory a/c and it had 3.64 gears. This car was bought from the guy who had it since 1972 and had never changed anything. I've always believed 'never say never' when it comes to car built in that era.
  3. Jim Weise

    Jim Weise GOT AIR?

    I can't swear to it, but I had always been under the impression that the Stage 1 rear gear was determined by AC or No AC. That was the limiting factor.. Even the 3.42 on the AC cars required the larger diameter pulley. The engineers determined that the 3.64 gear was incompatible with the AC pulley system, or maybe even the ac pump speed. Not sure if the issue was throwing belts, or over-speed of the compressor.

    I don't recall a transmission component to that decision. Seeing that rpm at road speed is the issue here, and that both stick and auto trans are 1:1 in high gear, not sure why 4 speed or auto would matter, from that viewpoint.

    I am pretty sure I built a 70 GSX with no air and a 4 speed, and it had the 3.64 gear.

    I am sure one of the more learned resto types will be along shortly to solve the issue.

  4. Jim Weise

    Jim Weise GOT AIR?

    Ah... Barry Grant, that explains it.. they came up with the "Idle-ease" system, that was incorported into the Ultra HP series carbs after Holley bought out Barry Grant. It's an idle air bypass that you access from the carb stud hole.

    See what size the venturi's are.. that's the key factor for jetting.

  5. Brett Slater

    Brett Slater Super Moderator Staff Member


    Numbers Muncie and 3.64 "ON" stamped 10 bolt posi rear - which was standard on 69 & 70 Stage 1 cars without air conditioning.

    My question in regard to highway driving was more of an example that the car has the born with gear ratio.

    I agree the factory tach is notoriously inaccurate but I definitely know the difference between 3.42 and 3.64 gears.

    At 60 mph, it's revving pretty well.

    Sorry to the OP for veering off track on this thread.
  6. DBS

    DBS Well-Known Member

    Correct. Rear was dependent on A/C, not trans.
    Brett Slater likes this.
  7. sporty-to-GN

    sporty-to-GN Well-Known Member

    IMG_20180105_234843.jpg IMG_20180105_234646.jpg IMG_20180105_234041.jpg IMG_20180105_233828.jpg
    Long day.

    .900 boosters
    1.56 venturis
    C12320 metering blocks
    56 cast in by the rear vent
    Last edited: Jan 5, 2018
  8. Jim Weise

    Jim Weise GOT AIR?

    So it's what Holley is now selling as an 850..

    Your pretty close to the out of the box jetting numbers, and assuming the carb is clean and in good condition, my suggestion to you is this: Synchronize the throttle plates:

    Close the front and rear throttle plates fully, back the screws off.

    Turn the screws until they contact the baseplate, but do not open the throttle plates.

    Open the primary and secondary throttle plates 1.5 turns, us the air bypass to set idle speed.

    Re-test.. if problem pesists, then you need to get an A/F gauge on it. Demons can be just that to tune, annular ones especially. Don't waste your time taking wild swings at jetting and accel pump tuning... it's a waste of time typically, and you can hurt your motor in the process.

  9. Bens99gtp

    Bens99gtp Well-Known Member

    Clearly a demond appears to have dowleg boosters if I recall correctly from all the number bouncing around in my gray matter this late....these numbers might be holley only sizes, i dont fully recall....with venturis of that size you could have an 830 it would have blade just under 1.75",can't remember the actual 850 would be 1. 75", but the 1000 cfm shared the same venturi size and butterfly. But the 950 at least 8n the hp used a smaller 1.3xx venturi with the large blade which because a lot of ppl said it can flow 950 with a smaller venturi than the 850, but I know blp has a 1050ish cfm 4150 with something close to a 1 4 venturi.

    I never measured my prosystems 4150

    If this is a newer build after holley took over I don't think they make 950 or 1000 cfm line.
  10. Bens99gtp

    Bens99gtp Well-Known Member

    Sorry for the info repeat, jw posted his reply as I was typing mine, did know it till I looked back at it
  11. Bens99gtp

    Bens99gtp Well-Known Member

    I find it funny, when looking on holleys site once switching to dowleg booster, it calls them 2x4 blower carbs........which if this a newer carb calibrated to be part of a pair on a blower that could have something to do with it
    Last edited: Jan 6, 2018
    crouchmtrsports likes this.
  12. 300sbb_overkill

    300sbb_overkill Well-Known Member

    That's an understatement! What a PIA a Demon carb is to set, even with an A/F gauge!

    Change the front jets and the WOT changes with them, there's no tuning the front and then tuning the back. Even if you disconnect the secondary linkage when you tune to primary, when you reconnect the secondary to tune that when you make a jet change the primary changes! Its kind of a guessing game even with an A/F gauge when jetting a Demon carb with better luck swapping out the front and back at the same time, give me a good old Holley any day over a PIA Demon!:mad::rolleyes:

    A Holley is SO much easier to tune hands down than any other carb I have ever played with. Then again I looked at the Demon like a Holley carb and tried to tune it that way because I'm by no means an expert tuner, maybe the Demon has a different procedure? With an A/F gauge though I can eventually get the ratios where I want them with either carb but takes WAY longer with a Demon! GL
    Mart likes this.
  13. sporty-to-GN

    sporty-to-GN Well-Known Member

    10-4, the secondary transfer slots do look a little over exposed. This carb is about 10 years old, I bet the difference in jetting and squirters is a factor of updates leading to the current models listed.
    From the looks of it, it's seen plenty of fire from below. I need to revisit cleaning the throttle body and main body passages.
  14. sporty-to-GN

    sporty-to-GN Well-Known Member

    IMG_20180107_222108.jpg Found a lot of the problem cleaning the main body. Both primary booster inserts were loose and came out pretty easily. One of the booster housings also feels loose in the body.
    In the pic of the body secondary metering block flange I'm pointing to some casting flash that's partially blocking the center hole. This should not matter since it's not equipped with a secondary PV, right? IMG_20180107_222229.jpg
  15. Bens99gtp

    Bens99gtp Well-Known Member

    On your flasHong I would say yes shouldn't matter......that's the passage engine vac comes up to basically to duck the PV closed.......since no valve no issue.

    I stand corrected when I though those were down leg......they are clearly annular....that pic shows a lot with annular boosters cause of their bigger size they will cause the same setup carb to be smaller cfm than compared to do leg. They do distribut the fuel better. I have never had a carb with annular boosters........I don't know if they receive signal sooner or take a lititle longer to get signal coming through and pull and shear fuel.
  16. sporty-to-GN

    sporty-to-GN Well-Known Member

    Driveability is much better after a few drops of loctite to all 4 booster inserts and swaged bases.
    MSD is in, 15° and 35° @2500.
    Transfer slots squared at 1/2 turn.
    Floats set to the center line per BG.

    AFR awaiting installation.

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