Announcement

Collapse
No announcement yet.

adjusting 4 corner idle on #4779-9 holley 750dp

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • adjusting 4 corner idle on #4779-9 holley 750dp

    having some minor issues trying to get a slight off-idle bog possible lean tip in ,i've got the a/f screws right now about 3/4 out but it did idle better at 1 turn out originally but slight rich sensation "eyes watering" but not very bad but noticeable . Probably went the wrong way in adjusting the carb but tried to solve the lean tip in first so changed the pump cams from the pink cams to a red #1 position primary and orange #1 secondary . still noticed a slight tip in possible lean condition while driving ,also while driving if i slowly got into the throttle the tip in issues were not as noticeable

    So i thought maybe it's now a pump shot issue so tomorrow i'm going to try a going to a #31 squirter from the stock #28 on the primary and leave the secondary alone as it is a #31 ,hopefully this may help .Now back to the a/f screws i know they all need to be equal so the idle circuit works at it's best . I been doing alot of reading on different websites and it seems a/f is anywhere from 1/2 to 3/4 out ,some have posted even 1 turn out and another mentioned 1/4 turn out

    Now i do have pretty large cam which is 257/269 @ .050 so vacuum is not all that much maybe 8" hg at most at idle so that can cause some tuning issues .so where would i start to get rid of this tip in issue ???
    "if it's too loud you're too old !!! "sigpic

  • #2
    It depends on the idle feed restriction size but 3/4 to 1-1/4 out should be fine. With that size of a cam how far are the throttle blades open at idle? How much of the transfer slot is exposed? Do you have holes in the throttle blades to help it idle? Have seen ALOT where people have the blades open so far it isn't on the idle circuit anymore to keep the idle up. This can cause a rich idle and effect tip in. Going up to a 35 squirter may help on the primary side and I generally use the pink cams. I'm no carb expert just fool around on some local stuff.
    Nick Smithberg
    www.smithbergracing.com

    Comment


    • #3
      Do you have lock out timing if not check and see what your initial timing is... With that larger of cam I say 22*-25* initial timing will help then curve the dizzy for your total... the low speed air bleeds will help with fine tuning.... also with a large cam rich is the common at idle
      Drag week 2009 Quickest street rod
      Drag week 2010 Quickest street rod

      Comment


      • #4
        What power valve are you running? If you are running the factory 65's they are opening almost immediately after you touch the throttle and what you might think is a lean could really be a rich bog condition. I would go down to 45's, or possibly 35's.

        With the cam you have and the amount of overlap it has at idle, you may have to live with a rich idle a bit.

        If you have adjustable air bleeds, I would go to a larger sized ones on the slow speed side, the idle circuit. Remember the idle mixture screws only adjust the amount of premixed air/fuel going through carb to engine. To lean it out, you need to add more air. You can drill out the non adjustable ones using indexed drill bits.
        BS'er formally known as Rebeldryver

        Resident Instigator

        sigpic

        Comment


        • #5
          Tip in hesitation on a carb is due to the accelerator pump circuit not being rich enough, you may have to change the pump shot cam on the throttle linkage or increase the size the squirters, if that doesn't do it, then you might have to go to a 50cc accelerator pump.
          Last edited by BigAL; March 23, 2014, 12:12 PM.
          The Green Machine.
          http://s1.postimg.org/40t9i583j/mytruck.jpg

          Comment


          • #6
            timing set at 26 initial 39 total on a Mallory unilite mech adv and for the carb i'm running 6.5's front/rear 31 squirter front/rear and stock jetting 71 pri / 80 secondary and according to my vacuum gauge in my car i'm just at 8-8.5hg vacuum at idle which is 1100rpm .Carb idles great and motor really sounds alot stronger by the sound of the exh note from the tail pipes compared to my old Holley 750 . The issue is jut off idle in gear or in neutral i've got a flat spot / hesitation but if i rev it a couple times sometimes in neutral the bog is not noticeable and while driving if i'm easy on throttle input the bog/flat spot is also not noticeable

            when i had the a/f screws 1 turn out there was not that noticeable of a flat spot but a friend of mine who was helping said it was burning hi eyes because of the carb being fat rich . I myself didn't notice it being the pig rich seemed normal to me and the car was backed into the garage o i don't know !! . Now the carb i replaced that was on my motor was a older late 60's early 70's or original version #4779 similar to a #6109 Holley 750 with it's unique linkage design . On that carb since it was just a main body and throttle plate i used dual feed bowls and primary metering block and a standard secondary metering block w/no a/f screws . it had 70 primary and 80 secondary , #31 squirters front/rear , red cam primary and orange cam secondary and a 6.5 power valve . This carb ran awesome with no issues except for a few times with stuck needle/seat causing it to flood but it was a good running carb . oh and the timing was the same with 26 initial 39 total

            Now this was why i went with a newer #4779-9 750dp because of the success of the older one it replaced but i've never tried tuning a 4 corner idle set up and not sure why i'm having problems as i thought it would be a simple swap . Now reading more i've seen people plugging the rear power valve and going up 6-8 sizes in the rear could i do this to the new carb to get it running better since i would be running off the primary power valve ??

            "if it's too loud you're too old !!! "sigpic

            Comment


            • #7
              Originally posted by Scott Liggett View Post
              What power valve are you running? If you are running the factory 65's they are opening almost immediately after you touch the throttle and what you might think is a lean could really be a rich bog condition. I would go down to 45's, or possibly 35's.

              With the cam you have and the amount of overlap it has at idle, you may have to live with a rich idle a bit.

              If you have adjustable air bleeds, I would go to a larger sized ones on the slow speed side, the idle circuit. Remember the idle mixture screws only adjust the amount of premixed air/fuel going through carb to engine. To lean it out, you need to add more air. You can drill out the non adjustable ones using indexed drill bits.

              i tried a 3.5 and 4.5 pv on my old 750 and all it did was made it worse and almost allow no throttle input without it falling on it's face and this new 4779-9 has standard air bleeds not the scre in style
              "if it's too loud you're too old !!! "sigpic

              Comment


              • #8
                Originally posted by BigAL View Post
                Tip in hesitation on a carb is due to the accelerator pump circuit not being rich enough, you may have to change the pump shot cam on the throttle linkage or increase the size the squirters, if that doesn't do it, then you might have to go to a 50cc accelerator pump.
                the carb came with pink cams and after doing alot of reading the general consensus was tthat cam has an extremely lazy ramp profile and will cause flat spots also a pink cam has a max of 37cc either of the pump cam screw positions . The red cam i'm using on the primary side has a faster ramp but has 18.5cc in pos #1 and 20 cc in pos #2 . The orange cam i'm using on the secondary side has an even faster ramp speed and delivers 19cc in pos #1 and 24.5cc in pos #2
                Last edited by oldschoolcamaro; March 23, 2014, 12:43 PM.
                "if it's too loud you're too old !!! "sigpic

                Comment


                • #9
                  Fix the idle circuit first. If you can turn the idle screws all the way in and the car doesn't stall, you are getting fuel from somewhere you are not supposed to. Power valve or fuel coming over the boosters most likely the case. Could also be causing the eye watering condition. If no fuel comes out of the sight screws on the bowls, then the floats are good. If it's the power valve, then it will be wet behind it when you remove the metering block.

                  Part of your tip in problem could be from the transfer slots uncovered at idle. If so, you need to open the rear throttle blades a bit. There is a screw in the bottom of the base plate that pushes open the rear throttle blades. Most likely have to remove the carb to do this. Very tiny adjustments make big differences. If the idle speed is too high and the front idle speed screw completely backed off, you have gone too far. Your mixture screws should be near 1 1/2 turns out.

                  Now, the accelerator pump. You shouldn't use your power valve to fix your lean out condition at tip in. Your 6.5 power valve opens 1.5 hg in below idle vacuum. It's opening almost immediately off idle. That's why I recommended a 4.5 or 3.5. First, make sure it squirts fuel at the slightest movement of the throttle linkage. I have seen this a lot. Then, maybe go up to a 35 or a 37 pump nozzle. If you still have a problem, maybe try the blue or green cams.


                  BS'er formally known as Rebeldryver

                  Resident Instigator

                  sigpic

                  Comment


                  • #10
                    Originally posted by Scott Liggett View Post
                    Fix the idle circuit first. If you can turn the idle screws all the way in and the car doesn't stall, you are getting fuel from somewhere you are not supposed to. Power valve or fuel coming over the boosters most likely the case. Could also be causing the eye watering condition. If no fuel comes out of the sight screws on the bowls, then the floats are good. If it's the power valve, then it will be wet behind it when you remove the metering block.

                    Part of your tip in problem could be from the transfer slots uncovered at idle. If so, you need to open the rear throttle blades a bit. There is a screw in the bottom of the base plate that pushes open the rear throttle blades. Most likely have to remove the carb to do this. Very tiny adjustments make big differences. If the idle speed is too high and the front idle speed screw completely backed off, you have gone too far. Your mixture screws should be near 1 1/2 turns out.

                    Now, the accelerator pump. You shouldn't use your power valve to fix your lean out condition at tip in. Your 6.5 power valve opens 1.5 hg in below idle vacuum. It's opening almost immediately off idle. That's why I recommended a 4.5 or 3.5. First, make sure it squirts fuel at the slightest movement of the throttle linkage. I have seen this a lot. Then, maybe go up to a 35 or a 37 pump nozzle. If you still have a problem, maybe try the blue or green cams.


                    was able to get it to run alot better today by installing a #31 squirter as almost all of the stumble is gone so i'm going to get a #35 and try that as i know it will help even more . Like i mentioned previously i had no problem tuning the old #4779 750dp that was on the motor and getting it to running really good . This is the first time i've tried messing with a 4 corner idle set up so it's been a major headache trying to get it to run right

                    On my old 750 i tried a 3.5 and 4.5 pv and all that did was not allow any throttle input without it falling on it's face "stumbling" and kept the 6.5pv as it ran very well for 4 years set up like that . So i know going to a 3.5 or 4.5pv in this new 750 it will do the same . also since i'm new to 4 corner a/f i think i messed up and didn't set ea screw the exact same so that may also be my problem as i think the rear a/f screw are maybe 1/4 out while the fronts are 3/4 out

                    i know for a fact the 2800 stall i've got is to tight so that doesn't help the idling in gear and that's why i put it in neutral at stop lights plus i do all my carb tuning as if i had a 4 spd manual . Today while idling around and watching my vacuum gauge it was 10" hg but the moment i got into the throttle it was down to 8-8.5hg
                    "if it's too loud you're too old !!! "sigpic

                    Comment


                    • #11
                      so much for it running good !!! , went to start it after sitting for a week in the garage and it acted like no fuel in the lines or carb as it refused to start after cranking the engine over quite a few times . old carb started with just 2 pump of the throttle so i did the same with this carb and nothing !!!! ,also i couldn't get it to idle for crap and kept trying to die . again wouldn't take any throttle input /tip in until the motor came up to temp but even after it got warm the idle was really strange . It acted like someone screwed the idle speed all the way closed so it wouldn't idle even though idle was set last week at 1100rpm and all was fine and idled nicely and ran great . i turned the idle up and it was running okay but after a couple minutes it was acting like the idle was set to low and wanted to die

                      Again playing with all (4) a/f screws now this time with a vacuum gauge no matter what i tried i couldn't get a clean idle ,even played with the floats and that didn't help . Now why would this carb run good a week ago and then sit for a week and run like crap !!!! ,i'm so pissed at this carb as my old 750dp ran great and this one has been nothing but a nightmare to tune . I did call Summit and they're going to warranty the carb so i 've got to pull it off and send it back

                      even though i'm sending it back any idea why this carb was a PITA to get it to run right compared to my old Holley 4779-0 750dp
                      "if it's too loud you're too old !!! "sigpic

                      Comment


                      • #12
                        I'm figuring your secondary throttle blades were not open enough, causing you to open the primaries to far to get it to idle, which uncovered to much of the transfer slots, which caused fuel to be drawn off the main jet circuit. If you turn all 4 idle mixture screws in and the car still runs there is only two ways this happens, one you have a blown power valve or two the primary throttle blades are open to far causing fuel to be drawn though the main jets(boosters). And I guess I should say improper float level can cause this to, but I'm sure you had that right. If I remember right you don't want more than .060 of the transfer slot showing, I usually set the secondary throttle blades open to that point and then do the same on the primaries. At that point the motor will usually idle higher than you want so can just adjust the primary side to idle it down. By the way if it take more than one turn to get to your desired idle, close the secondary throttle blades by a 1/2 turn, this will make it so you only have to adjust the primaries by a 1/2 turn, basically equaling out how far the front and rear throttle blades are open. And one more thing, if the motor idles lower than were you want it with the initial setting of both throttle blades showing .060 of transfer slot you'll need to drill holes in your throttle blades to allow more air into the motor to raise the idle.
                        Last edited by BigAL; March 29, 2014, 04:35 PM.
                        The Green Machine.
                        http://s1.postimg.org/40t9i583j/mytruck.jpg

                        Comment


                        • #13
                          Originally posted by BigAL View Post
                          I'm figuring your secondary throttle blades were not open enough, causing you to open the primaries to far to get it to idle, which uncovered to much of the transfer slots, which caused fuel to be drawn off the main jet circuit. If you turn all 4 idle mixture screws in and the car still runs there is only two ways this happens, one you have a blown power valve or two the primary throttle blades are open to far causing fuel to be drawn though the main jets(boosters). And I guess I should say improper float level can cause this to, but I'm sure you had that right. If I remember right you don't want more than .060 of the transfer slot showing, I usually set the secondary throttle blades open to that point and then do the same on the primaries. At that point the motor will usually idle higher than you want so can just adjust the primary side to idle it down. By the way if it take more than one turn to get to your desired idle, close the secondary throttle blades by a 1/2 turn, this will make it so you only have to adjust the primaries by a 1/2 turn, basically equaling out how far the front and rear throttle blades are open. And one more thing, if the motor idles lower than were you want it with the initial setting of both throttle blades showing .060 of transfer slot you'll need to drill holes in your throttle blades to allow more air into the motor to raise the idle.
                          This 4779-9 was adjusted the same as my old 4779-0 and my old carb ran better than the new one
                          "if it's too loud you're too old !!! "sigpic

                          Comment


                          • #14
                            I've never had issues with Holley carbs on this motor and have had dual 660's , dual 450's even a single 850 do and many 750's with no driveability issues until going with this 4779-9 Holley 750dp
                            "if it's too loud you're too old !!! "sigpic

                            Comment


                            • #15
                              Originally posted by oldschoolcamaro View Post
                              This 4779-9 was adjusted the same as my old 4779-0 and my old carb ran better than the new one
                              You can go to Holley's site and look up those carbs, it will have a breakdown of the jets, air bleeds, power valves, etc.. used in each carb, maybe you can find the difference there.

                              http://www.holley.com/data/TechServi...%20Listing.pdf
                              Last edited by BigAL; March 29, 2014, 08:02 PM.
                              The Green Machine.
                              http://s1.postimg.org/40t9i583j/mytruck.jpg

                              Comment

                              Working...
                              X