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Carb Tuning Success Story: Part Deux

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  • #1

    Carb Tuning Success Story: Part Deux

    I ended up dropping the float levels to 26mm as suggested and it definitely cured one issue: the need for throttle upon start-up. As for my slight stutter upon initial acceleration, I'll chalk it up to my errors in tuning. I do have one size bigger main jets in (140), but I'd rather leave those be. I know some have mentioned the pilots (mine are 42.5), but I think I'll practice some patience and just ride till I get some more knowledge on what's going on. One thing to not, after a five-minute ride, initial color on plugs are tan. And, more answers to any other questions is after that blip, throttle is beautiful through redline.

    My goal for this tune are two things: elimination of stutter upon take-off, and better gas mileage.
    1979 XS1100F
    2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.
    Tags: None
  • #2
    Originally posted by IanDMacDonald View Post
    I ended up dropping the float levels to 26mm as suggested and it definitely cured one issue: the need for throttle upon start-up. As for my slight stutter upon initial acceleration, I'll chalk it up to my errors in tuning. I do have one size bigger main jets in (140), but I'd rather leave those be. I know some have mentioned the pilots (mine are 42.5), but I think I'll practice some patience and just ride till I get some more knowledge on what's going on. One thing to not, after a five-minute ride, initial color on plugs are tan. And, more answers to any other questions is after that blip, throttle is beautiful through redline.

    My goal for this tune are two things: elimination of stutter upon take-off, and better gas mileage.
    With tan colored plugs if in the 4-5K cruising range sounds like your real close to correct. With some final tweating on carb-sync(don't forget to flip throttle so stops hit hard to seat the sync screw threads and re-check or set repeating a couple times to get things to stabilize and stay the same), and mixture settings, should help to keep that stupid grin that only you know why exists. Ride safe, Brant.
    81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.

    Comment

    • #3
      Some homework done . . .

      Okey dokey, got out to the garage today to do some homework for Rasputin. A couple of questions he asked were the following:

      1. What are the current settings?
      2. How many turns from soft seat to go from white to blue?
      3. How many turns from soft seat to go from blue to yellow?

      Answer to question number one:

      Cyl. #1: 3 3/4 turns
      Cyl. #2: 3 1/2 turns
      Cyl. #3: 3 1/4 turns
      Cyl. #4: 3 turns

      Answer to question number two:

      Even at soft seat, flame color was blue. I had to turn it quick, otherwise the bike stalled out.

      Answer to question number three: On cylinders #1 and #2, I turned the screws almost all the way out before I started seeing change in color (broken tips or too small pilot jet?) On cylinders #3 and #4, I started seeing yellow between a blue spark (every other half second) after 4+ turns.

      I did the plug chop and took pics of the plugs. The first set of pics are how the plugs were on a cold engine from a couple days ago.

      Cyl. #4:

      Cyl. #3:

      Cyl. #2:

      Cyl. #1:


      The second set of pics are running the bike in WOT on the highway with immediate engine shut-off.

      Cyl. #4:

      Cyl. #3:

      Cyl. #2:

      Cyl. #1:


      The third set of pics are running the bike in 5th gear @ 2k rpm for two miles @ 20+ mph.

      Cyl. #4:

      Cyl. #3:

      Cyl. #2:

      Cyl. #1:


      Letting the bike idle for five minutes in the garage with a box fan in-front of it gave me the same results as the first pic. I cleaned the plugs after each pull.

      As of now, I am using 140 mains, 42.5 pilots, with a suggested 26mm float height. I am thinking about raising the height back to stock setting.

      Questions? Comments?
      Last edited by IanDMacDonald; 09-17-2013, 07:23 PM.
      1979 XS1100F
      2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

      Comment

      • #4
        Pic of #4 cylinder on the second set of pics is wrong, but the others were just like #4, so you have an idea as to what it looks like.
        1979 XS1100F
        2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

        Comment

        • #5
          That's pretty close. I would call that rich to the lean side, or lean to the rich side, if that makes any sense to you.

          I've always found a stutter on acceleration to be an issue in the pilot circuit.
          Greg

          Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

          ― Albert Einstein

          80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

          The list changes.

          Comment

          • #6
            Originally posted by BA80 View Post
            I've always found a stutter on acceleration to be an issue in the pilot circuit.
            Ehh, this "stutter" is from a bad tune, not something native to the bike. I got something going on, and I have all the patience in the world to fix it.
            1979 XS1100F
            2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

            Comment

            • #7
              The plugs all look pretty close so obviously the sync is good, what other tuning issue would you think it is?
              Last edited by BA80; 09-17-2013, 08:06 PM.
              Greg

              Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

              ― Albert Einstein

              80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

              The list changes.

              Comment

              • #8
                Aha, that's where you old heads come in! I don't know without really tearing into these carbs. Broken mixture screw tips? (They did not look broken, but they did not look like needles either). Maybe it needs a bigger pilot jet?

                The thing is, I go with my gut, and my gut tells me that if it ran great prior to the mechanical advance switch with same jets, why would it not run the same after? I really don't think it is a jet issue. Clogged jet issue? I blew out the mains and the pilots. Clogged passages? Now, that could be a possibility.
                1979 XS1100F
                2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

                Comment

                • #9
                  One sign that I know that something is not right: When I pull the choke all the way out, the bike does not jump to 3k+ like it did prior to advance switch.
                  1979 XS1100F
                  2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

                  Comment

                  • #10
                    It's really hard to say without hands, and ears, on experience. A lot of people think that the power lag from 1000 to 3500 on these engines is a stutter. I can't say for sure without experiencing it first hand what may be going on.

                    Your plugs look good, that's all I can actually say for sure.
                    Greg

                    Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

                    ― Albert Einstein

                    80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

                    The list changes.

                    Comment

                    • #11
                      Originally posted by IanDMacDonald View Post
                      One sign that I know that something is not right: When I pull the choke all the way out, the bike does not jump to 3k+ like it did prior to advance switch.
                      THAT, really sounds like an issue with the carbs.
                      Greg

                      Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

                      ― Albert Einstein

                      80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

                      The list changes.

                      Comment

                      • #12
                        Yeah, Rasputin wants me to pull the carbs and check the diaphragms. I may do that tomorrow. Now I'm wondering if I should leave the float height where it is, or set it back to stock.
                        1979 XS1100F
                        2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

                        Comment

                        • #13
                          You can check them but the diaphragms wouldn't cause a stutter I wouldn't think. A leaky diaphragm would just limit your RPMs because of fuel starvation.

                          A broken mixture screw would make it idle bad but wouldn't necessarily cause a stutter.

                          I'm betting on pilot jets. You don't have your signature filled out and I can't remember if I've asked you before (old age and senility) but are you sure those are Mikuni (genuine) jets in there. Particularly the pilots. These carbs are touchy about the pilot jets.

                          If all else is correct the float level needs to be also.
                          Greg

                          Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

                          ― Albert Einstein

                          80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

                          The list changes.

                          Comment

                          • #14
                            Yup, genuine Mikuni 42.5's. But, why would I need bigger pilot jets now, when I didn't prior to the advance swap?
                            1979 XS1100F
                            2H9 Mod, Truck-Lite LED Headlight, TECHNA-FIT S/S Brake Lines, Rear Air Shocks, TKAT Fork Brace, Dyna DC-I Coils, TC Fuse Block, Barnett HD Clutch Springs, Superbike Handlebars, V-Star 650 ACCT, NGK Irridium Plugs, OEM Exhaust. CNC-Cut 2nd Gear Dogs; Ported/Milled Head; Modded Airbox: 8x8 Wix Panel Filter; #137.5 Main Jet, Viper Yellow Paint, Michelin Pilot Activ F/R, Interstate AGM Battery, 14MM MC, Maier Fairing, Cree LED Fog Lights.

                            Comment

                            • #15
                              If you think it's the advance put it back and see if that fixes it. The advance doesn't kick in until about 3500 -4000 though. Unless it's installed wrong.
                              Greg

                              Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

                              ― Albert Einstein

                              80 SG Ol' Okie;79 engine & carbs w/pods, 45 pilots, 140 mains, Custom Mac 4 into 2 exhaust, ACCT,XS850 final drive,110/90/19 front tire,TKat fork brace, XS750 140 MPH speedometer, Vetter IV fairing, aftermarket hard bags and trunk, LG high back seat, XJ rear shocks.

                              The list changes.

                              Comment

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