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Fish carburetor fun & games...

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  • Fish carburetor fun & games...

    I got my Fish carburetor mounted and running after an extended bit of troubleshooting- had to correct some problems. I'll be posting some pics later along with info on solving flooding & linkage difficulties.

    I've taken a couple of road trips so far to adjust mixture- 1st outing it was running a bit rich, today's plugs looked better. Hopefully I'll match or exceed the 13 Mpg I was able to get out of the Ball & Ball.

    I was able to idle the engine at ~ 200 Rpm- THAT never happened with the B&B! Plug coloring is identical on center and end cylinders. Lugging is even better, and I can do 2nd (and even 3rd gear ) starts with the flathead- the B&B didn't like 2nd gear starts at all. Acceleration is pretty snappy- all seems good so far!

  • #2
    That is really interesting. It would be fun to see some pictures.
    Power Wagon Advertiser monthly magazine, editor & publisher.


    Why is it that the inside of old truck cabs smell so good?

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    • #3
      Originally posted by maineSS View Post
      I've taken a couple of road trips so far to adjust mixture- 1st outing it was running a bit rich, today's plugs looked better. Hopefully I'll match or exceed the 13 Mpg I was able to get out of the Ball & Ball.
      How is it that you managed to get 13 MPG out of the B&B? Does that number reflect a bunch of tinkering, or is it just a case of normal driving. The best I have seen has been 12MPG and that was on an extended steady state cruse, which is nothing like the around the town driving I usually do.

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      • #4
        I'd bet on better mileage and probably fourth gear starts with an MSD 6a ignition added to the mix...
        I put one on my old Toyota Land cruiser (low compression ratio 2F 6 cylinder)
        It would NOT stall...

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        • #5
          The library was closed for some work last week, so I didn't have an opportunity to post- now we can start. The B&B 13 mpg came after mounting the radial Yokohama Geolander tires- that added about 2 mpg over the bias-ply Super Swampers, and gave a better highway ride.

          Initially I had bigtime flooding problems when I bolted up the Fish M-3- I'd see a lake of gas 1/8" deep in the intake before it warmed up and stalled out rich. The problem was the ball type inlet valve used by the Fish (pic #1)- it just couldn't hold pressure. It was supposed to operate between 3 1/2 to 4 1/2 psi, but it would slowly leak down to zero when I finally tested it. I tried regulating fuel pressure with a dial-type regulator, which was a complete waste of time- DO NOT rely on these! I bought a Holley 1-4 psi unit (pic #2) which was very reliable, but the ball valve just kept leaking.

          I finally took the carb off and started testing inlet valve popoff pressures and fuel levels. The Fish has a fuel level plug, which makes testing handy- 1/32" changes are significant in carb work.

          When you do fuel level testing, the carb must be, well, level. THAT will never happen on a vehicle, so it's better to set the carb on a surface that can be cross-leveled -I used a piece of shelving with shingle shims (pic #3). More to come...
          Attached Files

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          • #6
            After things were levelled up, I filled the carb thru the inlet til it wouldn't take any more (pic#4). Then, I connected my Silverline vac/pressure pump to the line (which still had gas in it), and slowly brought the pressure up to the 5 psi fuel pump pressure I had observed in earlier tests (pic #5). The mechanical flathead pump produces~ 4-5 1/2 psi. You want to be sure the pump is on pressure, because inhaling gas will eat the seals, and the pump body if it's plastic- the Silverline is metal.

            If the valve holds, check fuel level (pic #6). If fuel doesn't dribble, out check the plug threads with a piece of tissue laid across them- if that wets out, you're good, if it stays dry, you're likely too low. More tomorrow...
            Attached Files

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            • #7
              Something to keep in mind as we leave the test section is to make sure your gauges give a reliable reading and agree with each other. I used my Silverline tester and a fuel pressure/vacuum gauge- both of which agreed with each other. I also bought a small Mr Gasket fuel pressure gauge to mount on the carb- it read 2 lbs low compared to the others. The replacement also read 2 lbs low, and the tech at Mr Gasket advised me to try another company's gauge! Not checking stuff like this can cause bigtime problems- trust nothing before you verify!

              I finally gave up on the original Fish inlet valve, and made a replacement with a Quadrajet needle & seat fitted into a modified JIC adapter (1/8" female pipe to 1/4" flare)-pic #7. The nose of the flare end was cut back to the threads, then it was bored out to .272" and threaded internally for 5/16 x 24 tpi threads to accept the Quadrajet seat (pic #8). The seat had to be turned down 30 thou to fit thru the threads in the float chamber- from .407" dia to .377". The thread pitch on the JIC adapter needs to be 20 tpi to fit the carb- check that before you buy it.

              The quadrajet needle/seat assembly is the Edelbrock "offroad" item, PN 1465, available thru Summit and Autozone in a pack of two. The needle has a spring-loaded pin that keeps it seated all the time, some fuel pump pressure is used to overcome it when fuel level drops. I took the spring out and epoxied the pin in place (pic #9), since I am not presently using the truck offroad in extreme off-level situations. The inlet dia is .0935" compared to the Fish inlet's .118", but fuel volume isn't a problem. Unfortunately, you'll have to wait for pics #8-9, floppy/computer problems have struck!
              Attached Files

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              • #8
                Here's pic #8- what I did to the original Q-jet seat and JIC flare fitting, and pic#9- the spring-loaded needle compared mine with the pin epoxied in place.
                Attached Files

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                • #9
                  Pic #10 shows the float position at the proper fuel level- the arm is perpendicular to the chamber wall. Fish specified the float "square with the arm, and the arm square with the float chamber wall". Some people bend the arm to get the fuel level right, but I use shim stock epoxied to the arm (pic 11)- much finer control. The piece in the pic is .008".
                  Attached Files

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                  • #10
                    Pic #11 shows what can happen if you don't wash out the inlet valve assembly before placing it in service. The black bits in the fuel are rubber scraped off the inside of the fuel line, the white bit is thread sealant, and there are frequently bits of metal, especially with new threads. These will keep your needle from seating, and can find their way into tiny little passages in other carbs, which will cause many strange problems. I run gas both ways thru the inlet valve prior to screwing it into the carb body, and swab dish soap on the inside of the line before pushing it on. I also avoid multi-barb fittings like the one shown in pic #12. Use a single-barb, and file off the edge of the barb with a fine file (pic #12)- you'll be a LOT happier on your test drive (don't ask how I know this...).

                    Certain carbs have in integral fuel filter, which is a good way to stop this problem, it should also be backed up with a good inline filter. I've been looking for a filter that would screw into the inlet elbow AND be compact enought to fit under the air filter- still looking. The Fish has large internal passages, so trash in the fuel usually makes it run pig-rich from a leaking needle. The other thing that can make it run rich is shown in pic #13- too big a gap between the fuel pickup arm and the fuel chamber wall. This gap needs to be as small as possible, it's set by shims on the throttle shaft. The Fish directions mentioned painting machinist's dye on the chamber wall and setting the clearance so the arm barely touched the dye layer. If the arm or throttle shaft is bent so it binds against the wall, excessive clearance will be required, and the carb will run rich.
                    Attached Files

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                    • #11
                      One problem that surfaced during testing was bending of the throttle cable during acceleration (pic #13). This didn't happen during my fitting, because there was no fuel in the pickup arm chamber. The fuel caused enough extra resistance to bend the cable, causing really unpredictable acceleration.

                      We fixed this by cutting out the 2 5/8" section of cable with the threaded endpiece and replacing it with 2 5/8" of 1/16" stainless Tig rod with a new endpiece(pic #14). Now the cable is stiff where it needs to be, and flexible elsewhere. Driveability is now MUCH better.

                      I tuned the idle & Intermediate circuits according to directions, and ended up tuning for Economy after checking plugs. Acceleration is much better than the Ball & Ball, and I can run the idle down to 200 rpm- very smooth. Somewhere around 1-150 rpm it will just die- no shivering & shaking like the B&B does around 500 rpm. I set it for 700 rpm to insure adequate bottom end oiling on my tired engine. Still getting 13 Mpg.

                      I just bought a wideband O2 sensor (PLX Devices), and will be tuning the full-throttle circuit- stay tuned.
                      Attached Files

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                      • #12
                        Maine, do you think there are any improvements to be found with the intake manifold?

                        And I am excited to hear what you discover with the oxygen sensor information..

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                        • #13
                          The stock PW intake encourages flow to the center cylinders at the expense of the end pairs, which shows up on the plugs with my stock carb. The Fish appears to have better atomization, because the plugs have more uniform coloration between middle and end cylinders. It's one of the big reasons for the Triple Carb project- to maximize intake flow.

                          The Oxygen sensor should solve my hesitation on acceleration question with the B&B- is it rich or lean? I'm getting a shot from the accel pump, but it's either too much, or isn't atomizing effectively. It shoots across the throat of the carb, thru the main jet opening in the center wing, and hits the far wall.

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                          • #14
                            Great stuff!
                            Power Wagon Advertiser monthly magazine, editor & publisher.


                            Why is it that the inside of old truck cabs smell so good?

                            Comment


                            • #15
                              Maine, are you still running the fish carb? I just mounted a newer one made by mike brown in the eighties on my m37. After some fiddling I have it almost dialed in, Tremendous power increase over the carter.

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