1. MomsDuster

    MomsDuster FABO Gold Member FABO Gold Member

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    Hey folks, just going to throw this out there. Posted on a different forum and thought why not here too.

    I'm looking for some direction in a lean condition at cruise. I suspect it is related to the transition between the end of the transition slots and the beginning of the mains coming on. I can feel and hear the engine going lean and flat in the cruise range of 50-60mph.
    MPH RPM AFR
    35 1500 14
    45 1900 15.5
    55 2250 16.5-17
    65 2800 15
    70 3050 14.5
    It runs and feels good in the 14-15 afr cruise range.

    The car/engine specs:
    440 Dodge, 10.0 CR, iron 915 closed chamber heads with chambers cleaned up and mild porting. 231/237 @ .050 110 lobe separation 106 ICL, Weiand 1987 Hi-Ram Tunnel Ram w/2 ProForm 750 DP, 3000 stall and 3.23 gears.
    It runs really well and am very happy with it overall. Its just that lean area that bothers me at this point, it just sound and feels "off" there. I'll throw in that the timing is 19* at idle and has a fast curve, all in by 2300 rpm. I am running vacuum advance (ported at this time). I've tested with the vac can disconnected thinking maybe there was too much timing at those cruise speeds but the change (if any) was really unnoticeable. I have the secondaries wired closed as I am working on the cruise and PV circuit at this point. I will note that this is a 100% street driven car that occasionally gets a little romp on back country roads.
    The carbs:
    Primary Secondary
    .031 IFR .031
    .078 IAB .078
    .085 TSR .080
    .046 PVRC ---
    .036 MAB .036
    #74 MainJet #80

    I'll have the carbs apart this weekend to change PV's from 10.5 to 8.5 i believe the PV's are coming in a tic early (unrelated issue) so any suggestions are welcomed and appreciated.
     
  2. Rat Bastid

    Rat Bastid .004 light

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    What is your emulsion stack?
     
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    • ch1ll

      ch1ll FABO Gold Member FABO Gold Member

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      Do you feel that lean spot while accelerating through that point under load(driving)? Which leads me to my next question were all those readings you took under load?

      what I’m getting at is while accelerating its good but when get to cruising it goes lean. Does that sound right?

      consider this, it may be your intake plenum or lack of one as is the case with the Weiand high ram. Back in the day all pro stock cars ran them, they are designed for wot and acceleration. You may want to take a look at an edelbrock street ram. May solve your problem. And I know it’s not my shit, but your not doing your engine any good will double pumper carbs. Your washing oil off your cylinder walls and wearing your engine out.
       
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      • mbaird

        mbaird mbaird

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        I think your numbers look good for cruise but using 1 O2 sensor can throw you off . Maybe 1 or 2 cylinderss are leaning out ?
        I am having my engine dynoed on Nov 6th and plan on trying this out while I am there . This old guy locally actually had W2 dyno headers with individual O2 sensors and says he tunes for low speed as well as WOT.
        7175116D-224F-4A93-8F4A-1312B514EA95.jpeg 12F771C2-A362-4F8B-AFC6-5B6AAD4AA442.jpeg
         
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        • MomsDuster

          MomsDuster FABO Gold Member FABO Gold Member

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          .028 in 1st and 3rd from the top.
           
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          • Rat Bastid

            Rat Bastid .004 light

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            If you think it’s lean, open up the hole in the jet in the 3rd position to .032 and see what you get. That SHOULD make it get a bit richer, sooner.
             
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            • MomsDuster

              MomsDuster FABO Gold Member FABO Gold Member

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              Let me throw you a curve ball, my car has an aggressive nose up stance. (straight axle) the carbs are side mounted and have a 5.5* rearward slant where when the carbs are level the floats are adjusted just below middle of the sight glass. But the way the car sits, one side of the bowl the fuel level is at the top of the sight glass and the other side of the same bowl the level is just below the sight glass. Do you see that messing with the emulsion stack?
               
            • Rat Bastid

              Rat Bastid .004 light

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              Fuel level and having the carbs sitting with one side higher than the other will certainly affect emulsion and tuning. I’d have to think about it but you may be able to use a slant cut float to help that some. Obviously the best way to address that is to get the carbs mounted so they are sitting level in the car. Outside of that, slant cut floats (you can get them from BLP and you should be running those anyway) should help with getting the fuel level even side to side. You are dealing with pulling a 2 phase gas up the main well. The higher (or lower) the fuel level is, the easier or harder it is to pull that fuel/air up the well.
               
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              • mderoy340

                mderoy340 Well-Known Member

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                at 2250 your at the top of the idle/trans circuit - smaller IAB to fatten
                Basicly extend the idle circuit or start the main earlier. Both require smaller air bleeds.
                 
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                • MomsDuster

                  MomsDuster FABO Gold Member FABO Gold Member

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                  Update: Saturday I pulled the IAB's and found out they were .072 not the .078 that I had written down. I now remember doing that, but for the life of me can't remember if i actually tested afterwards. Then i went and broke the ever so important rule. I changed more than 1 thing at a time.
                  #1 Seeing that i used to run my vac advance with manifold vac i went back to that but left the fast curve in it,
                  #2 i put .070 IAB's in, adjusted mixture and idle, so the tune for most recent test is this:
                  P/S
                  .031 IFR .031
                  .070 IAB .070
                  .085 TSR .080
                  .046 PVR -
                  .036 MAB .036
                  74 main 80
                  10.5 PV
                  Emulsion stack from the top:
                  1) .028
                  2) blocked
                  3) .028
                  4) blocked
                  20* Idle timing 34* all in at 2300rpm and 14* of vacuum advance @ 15" of vac. vacuum can starts to add @ 6" of vacuum.
                  The results:

                  MPH RPM AFR VAC
                  35 1500 14 15"
                  45 1850 15 16"
                  55 2250 15.5 16"
                  65 2800 15 16"
                  70 3000 15 15.5"

                  Now there wasn't a big change but it was much better sounding and feeling. No longer feels flat in that transition area. The only negative thing was a popping out of the exhaust from say 40-60mph. I suspect that the timing is coming in too fast and is almost maxed out at 50mph. my next test will be to slow the curve back down and retest. It's definitely much better by the ear and butt dyno.

                  Sunday I slowed the advance curve by changing springs in the dist. I was unable to graph the curve at the time due to being by myself. Took it for a spin and the “popping” is all but gone and she’s running well. Smooth from idle to any cruise speed and stable at any cruise speed. Hopefully the weather mellows out this weekend and I can get some help graphing the timing curve. Probably put some fresh plugs in it and test some more. So far the butt dyno results are encouraging.
                   
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                  • mbaird

                    mbaird mbaird

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                    You need a timing light with a tach .
                     
                  • Rat Bastid

                    Rat Bastid .004 light

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                    If you want to start the mains earlier you use a bigger MAB not a smaller one.
                     
                  • Sublime one

                    Sublime one 72 Demon FABO Gold Member

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                    Trust the Butt Dyno!
                     
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                    • Bewy

                      Bewy Well-Known Member

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                      No, if you want to start the mains earlier, you use a smaller MAB.

                      I suspect your exh popping on decel is caused by a rich mixture, still burning when the exh valves open. With a TR intake, t/blades are probably closed more at idle [ compared to single 4bbl ] because you have 8 t/bores supplying air to the engine. That is going to apply a lot of engine vacuum to the idle cct on decel, pull extra fuel, making for a rich mixture.
                       
                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

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                      You guys argue over the effect of air bleed at circuit initiation like its a yes or no.
                      The reality is that it depends.
                      Before messing with the HSAB to tweak the main circuit's start up characteristic, first make sure its doing its job at the top end.
                      Then with emulsion correct and HSAB very close to providing the correction needed, a small increase in size should start the mains a little earlier and not cause a lean drift at high rpm WOT.
                      However this depends on how the air is bled into the main well.
                       
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                      • Rat Bastid

                        Rat Bastid .004 light

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                        I agree. As I’ve said before, as a GENERAL RULE (and 99% of the time) a bigger MAB starts the mains sooner and makes the fuel curve leaner at RPM. Bewy doesn’t get that. You have to be way off in emulsion to get a smaller MAB to start the mains sooner. Way off. I think the OP a said he has two .028 emulsion bleeds in the 1-3 position. That’s going to be fairly close. So a bigger MAB will start the mains sooner no matter how many times Bewy says it won’t. He read what Mike Urich wrote and we know he was never wrong.
                         
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                        • Bewy

                          Bewy Well-Known Member

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                          No, it doesn't depend....
                          It is not what I say, it is what the physics says.....
                          [1] And it is not just Mike Urich [ who was NOT wrong ] who is saying it...
                          [2] "A reduction in AB size reduces vacuum signal requirements & fuel flow is more easily initiated". Carter Carb book by Dave Emanuel, p.26.
                          [3] Decreasing the bleed size increases the pressure drop across the main jet, so more fuel is pulled through the main system, resulting in a richer mixture." Rochester Carburetors by Doug Roe, p. 10.
                          [4] Larger main jets richen the mixture, while larger MABs weaken it." Carburetor Performance Malcom Elston p.101
                          What Mattax & RB are getting confused with is when the system actually starts & what happens once it has started. Two different things.

                          For those following, a simple test will prove what I am saying. Put a straw in a glass of water & suck on it. Using a pin, put a tiny hole in the straw about the water. You will now have to suck a bit harder to get the water into your mouth. Now enlarge the hole considerably; you will have to suck a LOT harder to get the water into your mouth.
                           
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                          • Rat Bastid

                            Rat Bastid .004 light

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                            You completely ignore air speed and viscosity. The old straw trick fools many. A hole above fuel level acts differently than a hole with fuel over it.
                             
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                            • mbaird

                              mbaird mbaird

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                              That is actually a good point .
                              I have never thought of it that way.
                               
                            • j par

                              j par Well-hung Member

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                              What do the plugs look like?..
                               
                            • MomsDuster

                              MomsDuster FABO Gold Member FABO Gold Member

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                              Hoping to get a few miles on it this weekend, as soon as I do I’ll post some pics.
                               
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                              • j par

                                j par Well-hung Member

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                                I'm not sure if this has been covered but I noticed when adjusting my carburetors and also I noticed for instance Edelbrock dual quads they're not adjusted exactly the same... Or jetted exactly the same...
                                 
                              • Mattax

                                Mattax Just the facts, ma'am FABO Gold Member

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                                Yea. It's a way to introduce the concepts but only goes so far. None of these carbs are sucking fuel directly from the bowl. Both the air and fuel is coming through a series of restrictions. Furthermore the air, when properly introduced, reduces the density of the liquid fuel - hence the description of it as an 'emulsion'. Pretty much covered this in previous discussions about killbleeds and too many/too large e-holes in the more recent generation of 4150 and 4150 based carbs.
                                 
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                                • Bewy

                                  Bewy Well-Known Member

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                                  Mattax.
                                  'None of these carbs are sucking directly from the bowl.'
                                  Yes they are, through the m/jets. And you can remove the m/jets & you will get a horribly rich mixture. If the fuel doesn't come from the bowl, then how would fuel get to the booster/t.bores? The word sucking gets used a lot because it is easier to understand; fuel flows because of a pressure difference. Atmospheric pressure on one side of the jet & venturi vacuum [ depression] on the other side. VV is NOT the same as manifold vacuum.

                                  RB.
                                  Your statements confirm that you know little about how a carb works. The straw example I gave is a perfect simulation of how the AB works & how it's size affects the starting point of the main cct. For those interested in this, find a book [ or internet ] diagram of the main system of a carb & you will see the straw comparison is a perfect fit.
                                  'You ignore air speed'. Uhhhh no actually. You missed it. Suction & airspeed in a carb are mutually dependent. I wanted to keep the straw example simple so it was easy to follow. Air speed through the venturi where the fuel outlet is located is increased when the throttle is opened to increase engine rpm; at the same time, pressure in the venturi decreases. Atmospheric pressure in the bowl will at some point be higher & push fuel out of the nozzle. Adding an air bleed bleeds of some pressure, so more vacuum [ depression ] needs to be created in the venturi to get the fuel to flow. If the AB size is increased, the pressure signal is weakened & more vent vac is reqd to start the flow. This additional vent vac is created by opening the t/blades further to increase engine rpm [ & therefore air speed ]; flow starts. Larger MAB starts the system later [ higher rpm ] & smaller MAB starts at a lower rpm. The straw example is a perfect example of the system works. It is just physics.
                                   
                                • Rat Bastid

                                  Rat Bastid .004 light

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                                  Again, you ignore Larew and and viscosity. To do the straw trick you’d need two straws. But you know everything so there is that.
                                   
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