Transfer/Transition slot adjustment

Fuel and Air Systems

  1. Cuda416

    Cuda416 FABO Gold Member FABO Gold Member

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    Finally getting our 600 vac/sec "tuned" and wondering if there is a good way to set the transfer slot exposure while the carb is installed. Looks like the only way to set it is with the idle screw, but if someone touches that, it's gonna be off.

    Is the idea to set it off car, then install, and set idle using mixture and timing?
     
  2. 4spdragtop

    4spdragtop CONGRATS NORTH AMERICA! FABO Gold Member

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    • pishta

      pishta I know I'm right....

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      Start by adjusting it to form a perfect square, as tall as it is wide. Do you have 4 corner idle? Secondaries can be adjusted by small inset screw from under the carb. May be able to adjust primaries to square and then idle bypass with the secondary stop screw. Newer Holleys can have an idle bleed screw under the air cleaner stud.
       
    • Cuda416

      Cuda416 FABO Gold Member FABO Gold Member

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      It's adjusted to a square. 1850, 600 single metering block. Engine starts but won't idle. Idle mixture screws are 1.5 turns out.
       
    • Cuda416

      Cuda416 FABO Gold Member FABO Gold Member

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      Gonna check for a vacuum leak
       
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      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        Set timing first. Likely needs more advance than you think. You "should" be able to adjust secondaries open a crack if needed for more air. Don't leave mixture at 1 1/2 adjust them instead, engine up to temp, for best/ fastest/ smoothest idle and then just "touch" them towards the lean side
         
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        • Cuda416

          Cuda416 FABO Gold Member FABO Gold Member

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          We had it set to 20 btdc. Stock dizzy with the big spring removed
           
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          Pishta/Del have you covered.

          What cam, what engine,what heads, what cylinder pressure?
          If your cam is smaller than a 276/286/110, and your pressure is 185 or less, and we are talking a 360; then.
          I can idle mine down to 550 rpm in gear (4-speed), and pulling itself at 3.9 mph with 3.55s, a 750DP/AirGap, and
          timing of 5* BTDC.

          The point is this; when you get the fuel level right and stable, and the transfer slot to idle-port discharge synchronized just right, then she will act like a stocker. Remember this; the factory idle-timing on all the hi-compression 340s was? you guessed it, 5* advance.
          Pay attention to the Tslot sync and never mind the idle timing. Your engine will want up to ~30* of idle timing, the greedy beotch. But if you try to give her what she wants at idle, You will have other kinds of problems.
          I suggest to start at 14*, depending on what exactly your combo is. And you will need to slow the rate of advance,unless you have a very hi-stall TC.
           
          Last edited: Jan 8, 2021
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          • Mattax

            Mattax Just the facts, ma'am FABO Gold Member

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            Unless its a really radical cam with low compression, that's not a great starting point.
            It will start easier with less initial.
            It will run stronger with both springs.
            Discussion here Large RPM and Vacuum drop when shifting from park to gear

            Yes. Sort of.
            While the carb is off, measure and write down how far the slot gets exposed for every 1/4 turn of the idle speed/throttle stop screw from just touching.
            That way you can start and run fast idle with the throttle more open. Once its warmed up you'll be able to reduce the throttles to the .020 to .35" range.
            Even if it has a choke and fast idle, its good to know how much the throttle screws can be turned and still be within the t-slot working range.

            Good starting point for the mix scrrews
            The important thing is that the mixture screws provide some level of control when the engine is warmed up. So if they end up 1/4 turn out or 2 turns out isn't that important. it does provide some indication of how much fuel is coming the transfer slots.
            Make sure the fuel level is ballpark before getting too far along.

            Holley idle mixture screws
             
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            • Cuda416

              Cuda416 FABO Gold Member FABO Gold Member

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              Alright folks, first of all, thanks once again for all of the great info and assistance. You people never cease to amaze me.

              The engine, is a stock 5.9, junkyard motor, converted to carburetor and hei ignition with a distributor from @halifaxhops, BIG thanks to him by the way. We've done really nothing else but slap a 4 bbl on top of an air gap clone intake and call it good.

              My mistake on the timing, and it's mine alone, was because it "ran well(ish)" when the transfer slots were almost fully exposed and I had no idea. Reading posts here about the idle mixture screws doing nothing led me to that solution. My son took care of adjusting the throttle plates so they would actally close completely, then at the suggestion we move the timing back to stock (ish), we are now able to idle at around 650, and actually adjust the fuel mixture. Off throttle (stationary) is actually a bit snappy to our surprise.

              I've learned more in the last 36 hours about carburetors than I have in the other 51 years, and I've still got about 20 years to go. :)

              At this point, we're better but still a long way to go in a short amount of time.

              -=C
               
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              • Cuda416

                Cuda416 FABO Gold Member FABO Gold Member

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                Seems as @Mattax points out, having both springs in is a good idea. Not that I doubted it, but hadn't gotten to put the big one back in yet and it's dogging during acceleration. I believe the weight without a spring is helping pull the other weight with the lighter spring out faster than I want. Not what i was going for, but it makes sense now that I think about it. I guess it's possible one spring might be ok, if it's strong enough to overcome both weights, but then what's the point. Anyway, I'll be fixing that tonight.

                My plan...

                1. Fix the dist.
                2. Reset the xfer slot size. It's been "mucked" with again and I'm not sure where it is. Sure would be nice to be able to set the min closing from the top, then adjust idle off of that, but that's probably because I don't know what I'm doing really. :)
                3. Set the timing to "stock-ish" at ~6 initial
                4. advance timing, reduce idle screw per @318willrun method until it settles down.

                One thing I'd like to know is how to determine the total mech advance of the dist. The "T-bar" with the slots in it has the number 30 stamped into it as I recall, which seemed really high but then again, when it's set between 5-8 it runs "ok" so maybe it's right. if that's the number, then I don't need to worry about finding what it is. If not, how does one do that off engine and no distributor machine? Also, the advance pod has "7R" so I believe that means it can add up to 14 under load?
                 
              • pishta

                pishta I know I'm right....

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                The light spring is the 'hop out' profile of the distributor, the heavy spring is the higher RPM control on a Mallory, probably the same on a stocker. Its amazing what a tuned carb feels like when you get it 'right'. ie. how did it even run when it was so screwed up?
                 
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                • Cuda416

                  Cuda416 FABO Gold Member FABO Gold Member

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                  surprisingly well at lower rpm, lol. I'm sure that's because it partially advanced already with the combined weight pulling on that one spring.
                   
                • Cuda416

                  Cuda416 FABO Gold Member FABO Gold Member

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                  So, thinking about the xfer slot and how to get it into the ball park. Maybe I've read this somewhere before but let's say my engine is idling with the mixture screws all the way in. If I turn the idle screw until it finally dies, shouldn't that be right about where I want it? Then i can turn the mixture screws out a bit and start normal tuning?
                   
                • pishta

                  pishta I know I'm right....

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                  I'd shoot for transfer slots at square, idle screws out at 1.5 and the secondary butterflys adjusted to give you an acceptable idle, then mess with the idle screws but you must have enough adjustment in or out to have them be effective. You can adjust the primary idle screw but you are altering the transfer slot that you spent all that time trying to set. The 'holes drilled in the blades' does the same that the secondary throttle stop. does.
                   
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                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

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                    Yes. Yes.
                    With a combination you've created yourself there will be several iterations of trials as you tune it in.
                    Lean is more sensitive. So it's easier to turn the screws in small increments until the rpm or vac just begins to drop off. Then turn it back to where the rpm was strongest. I usually give each mix screw a 1/16 to 1/8 turn richer from that so it will be stronger when placed in gear.


                    Not knowing know what the junkyard 360 came out of, here's some generalizations.
                    While a 2bbl 318 was pretty efficient at low rpm, the 360s a little so, but the magnum versions and later heads probably a little more efficient.
                    The less efficient the engine is at idle, the more spark lead it will need.
                    A slighter hotter cam almost always hurts efficiency at idle - even the factory 4 bbls (pre-smog) have inital timing around 10 to 15* BTC.
                    However especially with the 4 bbl carb on them, they quickly gain combustion chamber efficiency above 1400 to 1800 rpm.
                    I'll post some examples of pre-smog factory timing curves below.

                    Since yours is idling nicely at 6*BTC at 650 rpm that seems like a good starting point.
                    You could try 4* at 650 rpm but that will probably require opening the throttles a little more to get the rpms back. If it does not require them to be open so much that .035" or more of the t-slots are exposed, it may be worth giving it try.
                    Likewise you could try 8 or 10* BTC at 650 rpm. If the t-slots are between .020 and .035 that might be worth pursuing. After fiddling with the idle mix put it in gear (if automatic) and see if the rpm and vacuum is stronger than the best tune it had at 6*BTC, 650 rpm.


                    Here's the range of factory timing for a '68 Plymoth 318 2bbl (initial could be set a little higher or lower based on fuel and altitude)
                    upload_2019-3-21_21-22-9-png-png.png

                    Compared with a '67 273 4 bbl. (initial could be set a little higher or lower based on fuel and altitude)
                    upload_2019-7-30_21-36-48-png-png.png

                    I chose these examples because they were not Clean Air Package engines.
                    Notice in both that rate of advance slows above 1400 rpm. That's the heavy spring with long loop engaging.

                    There's pictures here showing how the springs work on the weights and how they can be adjusted.

                    If the distrubtor you're using has a mallory YH advance, its done a little differently but concept is same.
                     
                    Last edited: Jan 13, 2021
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                    • Cuda416

                      Cuda416 FABO Gold Member FABO Gold Member

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                      Danng, once again, FABO folks provide. @Mattax I can't thank you enough for taking the time to help a guy out.

                      The engine is out of a 98 Durango. We converted it to carburetor and HEI ignition. We also swapped the timing cover for an LA and are running a small electric fuel pump. The cam has not been changed from stock so it's completely wrong for the application now.

                      We're running everything through 273 exhaust manifolds, in front of a stock 904 and an unknown factory lockup TC.

                      For good measure, we replaced the oil pump when we replaced the pan.

                      Running a holley 600 (4160) w/vac secondaries. The "typical" setup on top of an air gap clone.

                      Oil pressure at start is around 60, then settles to around 25-27 when warmed up. We're considering bumping to 10-40 or even 15-40 since we're in south TX and it doesn't really get cold here.

                      Engine lights up on the first turn.

                      One thing we notice is a change in engine rpm (increase slightly) when the fuel pump is running, which as I think about it now seems to indicate it's pushing fuel passed the needle valves, but there isn't any fuel spilling out the vent tubes so I'm not sure.
                       
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                      • RustyRatRod

                        RustyRatRod Lemmie see your b00bs. FABO Gold Member

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                        I've always compared the tech help at Holley to the emergency room. Just enough to get you movin again without bleedin to death.
                         
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                        • yellow rose

                          yellow rose Overnight Sensation FABO Gold Member

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                          LOL...funny...but incredibly true.
                           
                        • mbaird

                          mbaird mbaird

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                          Don't rule out a vacuum leak if the issue persists. I chased an idle/low rpm issue for over a year . I couldnt find a vacuum leak so I focused on carb/dizzy tuning with mixed success .
                          Finally I ordered Eddie embosed gaskets and Gasketcinch adhesive just to see if it might help .
                          Voila ! My engine idles much better and way smoother below 2000 rpm .
                          The leak must have been below the intake.. I even tried propane to find leak .

                          This is a 5.9 with Airgap intake and 222/229 @.050 .510 lift cam
                           
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                          • 318willrun

                            318willrun Utube channel 318willrun

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                            LOL... :D :D
                             
                          • Cuda416

                            Cuda416 FABO Gold Member FABO Gold Member

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                            Engine pulls 20Hg from the manifold. Not ruling it out, just laying that out there. it's definitely something to look at. Thanks!
                             
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                            • Mattax

                              Mattax Just the facts, ma'am FABO Gold Member

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                              The thing with the slots I call the 'slots'or athe 'plate' but IIRC Chrysler calls the governer.
                              I can't guess what the number might be on it but probably not 30.
                              9, 11, 13, 15 range are the most common. Some will be R others L, some with cut slanted which effects the rate of advance.
                              Anyway those are the maximum degrees of distributor advance. Double that for the degrees of advance on the engine. With an electronic distributor particularly, assume in actual use a few degrees less.
                              The vac arm you interpret correctly.
                              How To Limit and Adjust Chrysler Vacuum Advance Cans

                              To see the effect of changes without a distributor machine, use the engine, a timing light, and a tachometer.
                              measure and write down the timing from as low of rpm as you and then at a number of points at higher rpm.
                              I like pictures so I plot the points on a graph.

                              it's possible to ballpark changes by making a pointer and a degree wheel.

                              I think that 60 psi cold and 25psi hot at 650 rpm is great. As long as the pressure rises back to 60psi on the highway I'd stay with your current viscosity grade whatever it is.
                               
                            • Cuda416

                              Cuda416 FABO Gold Member FABO Gold Member

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                              Just addressing the total advance based on the slots quickly. I had it out the other day and measured them. My caliper told me 0.470, just shy of the measurement for 15, or as I understand it, 30 total so unless I have that wrong, it's what I've got to go by until I can take an actual measurement with a degree wheel. Oddly there are no marks on it whatsoever. I was surprised by that.,
                               
                            • Mattax

                              Mattax Just the facts, ma'am FABO Gold Member

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                              You got it right.
                              Leme take a quick look at my spreadsheet notes
                              edit:
                              yes that agrees with the measurements I've made as well the various articles.

                              If you've seen the video @yellow rose posted, it shows how the time used for electronic switching steals a degree or so every 1000 rpm. We really only see this after the weights hit the top of the slot. I only mention it as one of several reasons that the stamped number is not absolute.
                               
                              Last edited: Jan 14, 2021
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