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S&S carb jetting and adjustments.

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  • S&S carb jetting and adjustments.

    Just curious to see what other people are running on their S&S carbs. Right now I'm running a 74 main with a .295 int jet. I'll list my combo below. It's strange, I just can't seem to get it right. One day it's great, the next day it just doesn't want to run.

    S&S Super E carb w/74 main and .295 int.
    80 ci
    S&S Super Stock heads
    S&S 10-1 pistons
    S&S 561 cam
    V&H Longshots w/stock baffles
    Stock Ignition box
    Justin, HERD member 00016
    97 Fatboy

  • #2
    Welcome to the world of S&S carbs for street use.

    I ran one for years and had just that: Good days and bad days. Float level is critical.

    As well, I'd suggest running an aftermarket module for a better timing curve. You've got all this performance and a stock timing curve and a dual fire ignition. You should look at going to a single fire, which would suit your mods better.

    S&S is a great performance carb, but has a tendency to dump more then necessary fuel. If you lack the ignition to burn it all, that could be an issue.

    What plugs are you running as well?

    At a minimum: You'll be victim to the quality of fuel you run too, and that's probably got more to do with it then anything.......
    **Note: The technical info I provide is suggestive. I am not a perfeshunel.

    "No two motorcycles should be the same. Your bike should be based on your creativity, and whatever's going on in your life at that time..." Jesse James


    HERD Member #10

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    • #3
      I have a SE adjustable ignition sitting on the work bench, but my bike pings when it is installed. After trying all of the curves, setting my timing, and even trying a second box, I finally gave up and put the stock one back in.

      Plugs are the standard Champion that S&S recomends. I was just on NGK's web site crossing the Champion # to a NGK #(BPR5ES-11). I'm going to buy a set tomorrow and give those a shot.

      Fuel, I either run Shell or BP from around here. That's the best I can do here in Milwaukee. ( besides the race gas at the corner pump )

      I may go back to the 72 main and deal with the occ pinging on a hot day. It seemed to run better with the 72, but the plugs look better with the 74. And plugs don't lie. This sucks.....

      This is why I love Fuel Injection, (for cars) I have never played with it on a bike though.
      Justin, HERD member 00016
      97 Fatboy

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      • #4
        Originally posted by autotec View Post
        I have a SE adjustable ignition sitting on the work bench, but my bike pings when it is installed. After trying all of the curves, setting my timing, and even trying a second box, I finally gave up and put the stock one back in.

        Plugs are the standard Champion that S&S recomends. I was just on NGK's web site crossing the Champion # to a NGK #(BPR5ES-11). I'm going to buy a set tomorrow and give those a shot.

        Fuel, I either run Shell or BP from around here. That's the best I can do here in Milwaukee. ( besides the race gas at the corner pump )

        I may go back to the 72 main and deal with the occ pinging on a hot day. It seemed to run better with the 72, but the plugs look better with the 74. And plugs don't lie. This sucks.....

        This is why I love Fuel Injection, (for cars) I have never played with it on a bike though.
        Pinging is BAD. By no means go back to the 72 if it pings. I'm wondering if with a 74, you still may be a tad lean. How many turns out, with the 74 is your a/f screw?
        **Note: The technical info I provide is suggestive. I am not a perfeshunel.

        "No two motorcycles should be the same. Your bike should be based on your creativity, and whatever's going on in your life at that time..." Jesse James


        HERD Member #10

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        • #5
          Originally posted by Dave63 View Post
          Pinging is BAD. By no means go back to the 72 if it pings. I'm wondering if with a 74, you still may be a tad lean. How many turns out, with the 74 is your a/f screw?
          It only pinged on really hot days in traffic. My A/F screw is 1 1/4 turns out. I was thinking lean also, but you would think I would have made it better by going to the 74, but it feels like I made it worse. But then again, it seems to get better when I give it a little gas, and that would support a lean problem because of the acc pump dumping gas into the engine when I twist the throttle. Maybe I'll try a 76 and see what happens. Or maybe move up to a .310 int jet. This is too much to ponder when I'm at work. LOL.
          Justin, HERD member 00016
          97 Fatboy

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          • #6
            Also, it doesn't help I'm playing with my exhaust too. I rode it to work today with the baffles removed, and it was bad. It just didn't want to run. It screamed on the upper end, but there was NOTHING below 3K. With my baffles with the homemade restrictors, I had a ton down low, but nothing on the upper end. I received the replacement baffles from Ironhead shortly after I left for work, so I will get them in tomorrow. It's just amazing how much a baffle will effect the way it runs.
            Justin, HERD member 00016
            97 Fatboy

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            • #7
              Start by doing this: Write down every thing you do.

              To this day, I have written notes regarding every carb mod I've done and how it felt, regarding jetting, exhaust, main needle height, etc. I can always go back to what felt good, if I need to.

              With your S&S, if I'm correct, your accel pump is adjustable. You may have it set too rich.

              Running TOO lean can actually feel good at times, and give you a false performance (smappy throttle) but beware.

              At running your a/f screw 1.25 turns out, unless you're running rich, that's a good place. If the plugs look good, then start looking at accel pump settings.

              As for your main jet settings.... that's determined by how the bike feels at about 2500-3000 rpms, 5th gear and you floor it.

              If the bike seems to bog, but picks up when you let off for a second, you;re running to lean.

              If the bike seems to run out of fuel, but you can keep "pumping the thottle" and it seems to pick up, then you're running too lean. Go to a bigger main jet.
              Last edited by Dave63; 05-14-2010, 09:03 PM.
              **Note: The technical info I provide is suggestive. I am not a perfeshunel.

              "No two motorcycles should be the same. Your bike should be based on your creativity, and whatever's going on in your life at that time..." Jesse James


              HERD Member #10

              Comment


              • #8
                I will give it a shot. This gives me a good excuse to go out for a ride tomorrow. LOL. I think I may even try to fabricate a holder for my wide band o2 sensor, that way I can really see what it is doing under a load ect.... This is how I tune my snowmobiles, but I actually welded a bung into each pipe on those. On my bike, that would be pretty hard without damaging the look of the pipes. Either way, I have to get this figured out before next Thurs. Thanks again Dave.
                Justin, HERD member 00016
                97 Fatboy

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                • #9
                  Another question. Reading through the post again, you mentioned to nail it at 2500-3000K to test the main. At what RPM does it switch from the int to the main? I'm running 2200 at 60mph on the highway, I'm wondering if it's running off of the int jet at that speed. If it was, I could be playing with the wrong jet.
                  Justin, HERD member 00016
                  97 Fatboy

                  Comment


                  • #10
                    Well, the last 5 miles of my ride home was on 1 cyl. (most of the time) It also sounded like the front piston wanted to escape through the engine. I got home checked compression thinking the worse and was suprised to see both cyls at 180 psi. I also checked spark, and had nice blue spark on both wires. (new wires) The front plug was alot blacker than the rear and I found that kinda strange. When I checked them 40 miles earlier, both looked great. I'm hoping I fouled a couple of plugs due to running rich, but I'm not holding my breath. I'm going to reinstall the 72 main and a couple of new plugs tomorrow and hope it runs great. I still don't know what the noise was, but I'll look into that tomorrow. Wish me luck everyone, I really want to go to Herdstock.
                    Justin, HERD member 00016
                    97 Fatboy

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                    • #11
                      Well, I figured out why I can't seem to get it right. It turned out the be the needle and seat. I went to drain the bowl to swap the main jet again, and there was nothing in it. Then when I turned the gas on to see if anything was flowing, it really started flowing, right out under the bike. Went and bought a new needle and seat, swapped back to a 72 main, and all is well. My only guess is the needle would stick closed at times causing a lean condition, and open at times causing a rich condition.

                      I'm just hoping the engine isn't hurt, I'm guessing the noise was severe pinging. I couldn't pull over when it was happening because I was in a construction zone without any emergency lanes. So all I could do was be easy on it. I don't hear any noise now, but only time will tell.
                      Justin, HERD member 00016
                      97 Fatboy

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