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  • started tuning my carbs, got a problem

    I cleaned the carbs, have the idle screws 1.5 turns out and synced the carbs today. That new carb sync gauge set I got worked wonders... it was really easy. Got them all in line in a matter of minutes.

    So onto the problem. It sounds good, but I have a bad ear so I don't trust it, on a whim I put one of those non contact temp guns on each header pipe and #4 was pretty cold... was waayy colder than the rest of them. 1-3 where 600F and #4 was 250F. WTF! I did a leakdown test and everything looked good, only 3% loss. So I put my colortune on #4 and it was sparking but no color, no gas. Put it on #1 and it was the right orange/blue color. I had to turn the idle screw on #4 out almost 5 turns to get it gas and the right color.

    So I know I have to take the carbs back off, but what should I check? The float height and pilot jet?
    Last edited by thebottle; 05-09-2020, 12:28 PM.
    1980 XS1100SG
    1998 KLR 650

  • #2
    Looks like the pilot circuit is dirty.
    Clean the pilot fuel and air jets along with the carburetor passages.


    Float heights... 99 times out of 100 just setting the float heights by the book will get the fuel level in the carburetors where it's supposed to be but before you pull the carburetors do a fuel level check.

    You can dink around with float settings until the cows come home but at the end of a long day tweaking floats without busting any float pin posts it's the actual level of the fuel in the carburetors that's important.
    -- Scott
    _____

    2004 ST1300A: No name... yet
    1982 XJ1100J: "Baby" SS Brakes, '850 FD, ACCT
    1980 XS1100G: "Columbo" SS Brakes, '850 FD, ACCT
    1979 XS1100SF: "Bush" W.I.P.
    1979 XS1100F: parts
    2018 Heritage Softail Classic 117 FLHCS SE: "Nanuk" It's DEAD, it's not just resting. It is an EX cycle.

    Comment


    • #3
      Did you confirm all the sync gauges read the same?

      You can rotate them to see if you get the same results, or better yet, you can connect them all to the same cylinder simultaneously to be sure they read the same.
      -Mike
      _________
      '79 XS1100SF 20k miles
      '80 XS1100SG 44k miles
      '81 XS1100H Venturer 35k miles
      '79 XS750SF 17k miles
      '85 Honda V65 Magna ~7k miles
      '84 Honda V65 Magna 48k miles (parts bike)
      '86 Yamaha VMAX 9k miles

      Previous: '68 Motoguzzi 600cc + '79 XS750SF 22k miles +'84 Honda V65

      Comment


      • #4
        Originally posted by Radioguylogs View Post
        Did you confirm all the sync gauges read the same?

        You can rotate them to see if you get the same results, or better yet, you can connect them all to the same cylinder simultaneously to be sure they read the same.
        I must admit that I too am intrigued with a vacuum sync that apparently balanced out even when one carb quite obviously is not working.
        -- Scott
        _____

        2004 ST1300A: No name... yet
        1982 XJ1100J: "Baby" SS Brakes, '850 FD, ACCT
        1980 XS1100G: "Columbo" SS Brakes, '850 FD, ACCT
        1979 XS1100SF: "Bush" W.I.P.
        1979 XS1100F: parts
        2018 Heritage Softail Classic 117 FLHCS SE: "Nanuk" It's DEAD, it's not just resting. It is an EX cycle.

        Comment


        • #5
          Before you take the carbs off, are you able to do a running fuel check ?
          That procedure will reveal how much fuel each carb is getting.
          #4 float may be partially stuck shut.

          You may want to start with two turns out from lightly seated on the idle screws, but the color tune IMHO yields the best results after syncing.
          Last edited by Schming; 05-09-2020, 01:36 PM. Reason: Had this half written then got a phone call and BOOM !!! 3posts;-{)
          1980 XS1100G "Dolly G" Full Dresser (with a coat of many colors )
          1979 XS1100SF (stock-euro mods planned)
          1984 XV700L Virago (to be hot-modded)
          1983 XJ750MK Midnight Maxim (semi-restored DD)
          1977 XS650D ( patiently awaiting resto)

          Sometimes it takes a whole tank of gas before you can think straight.

          Comment


          • #6
            Just checked, and the gauges read the same if I move them to the same cylinder.

            When everything is 1.5 turns out, I can sync them but then #4 doesn't get fuel.

            At 1.5 turns and the carbs "synced" I can turn the sync screw between #3 + #4 until #4 gets fuel, but then #3 gets cold, and the readings are waaay off on the gauges then.

            Or at 1.5 turns with them again synced, I can turn the idle screw way out on #4 until it gets fuel, then resync them on that... but it doesn't seem like I should have to turn the idle screw that far out, right? So I'm leaning toward it being the pilot circuit on #4.

            Tomorrow I'm going to clean #4 again, and re-bench sync them, and go another round with it. Really want this running correctly this weekend so I can start on the other stuff that needs fixing like the master brake cylinder and suspension and then it's finally back on the road! Can't wait!
            Last edited by thebottle; 05-09-2020, 03:10 PM.
            1980 XS1100SG
            1998 KLR 650

            Comment


            • #7
              carb clean

              Hey Bottle,,,looks like the guys have it figured out
              1. dirty pilot,,,just shoot carb cleaner through it, and all the other jets
              2. pull the plug to see if its non fouled and gap is good, as exhaust pipe shows a fuel or firing issue
              3. maybe smack the carb a couple times on the #4 side before pulling them to see if the float was hanging up, if so, thats the culprit and a cleaning and gasket check
              4. pray to the carb gods

              Have fun, it will be worthwhile to get the beast roaring again, Mike in SUn Diego
              mike
              1982 xj1100 maxim
              1981 venture bagger
              1999 Kawi Nomad 1500 greenie
              1959 wife

              Comment


              • #8
                Almost forgot

                Almost forgot, HAPS BIRTHDAY 3PHASE ___Scott,, good to see you back on the XS, or rather XJ site, see you and Roo soon,,,,,Mike, Eagletom, Roo
                mike
                1982 xj1100 maxim
                1981 venture bagger
                1999 Kawi Nomad 1500 greenie
                1959 wife

                Comment


                • #9
                  Birthday's in June -- thanks, Mike!


                  1.5 turns is kind of lean for the late-model BS34 carbs, it should be closer to 3.

                  I wonder if the mechanical idle screws for the throttle plates are turned open too far open so the intermediate fuel clusters are exposed and feeding fuel at idle.

                  Of course it's not the only reason but it's usually why the idle mixture screws can be dialed way down like that without stalling the engine.
                  -- Scott
                  _____

                  2004 ST1300A: No name... yet
                  1982 XJ1100J: "Baby" SS Brakes, '850 FD, ACCT
                  1980 XS1100G: "Columbo" SS Brakes, '850 FD, ACCT
                  1979 XS1100SF: "Bush" W.I.P.
                  1979 XS1100F: parts
                  2018 Heritage Softail Classic 117 FLHCS SE: "Nanuk" It's DEAD, it's not just resting. It is an EX cycle.

                  Comment


                  • #10
                    Originally posted by 3Phase View Post
                    Birthday's in June -- thanks, Mike!


                    1.5 turns is kind of lean for the late-model BS34 carbs, it should be closer to 3.

                    I wonder if the mechanical idle screws for the throttle plates are turned open too far open so the intermediate fuel clusters are exposed and feeding fuel at idle.

                    Of course it's not the only reason but it's usually why the idle mixture screws can be dialed way down like that without stalling the engine.
                    I was thinking the same thing Scott. No. 3 is by the throttle screw. 4 is synched to 3. 1 and 2 are synched to 3 (throttle screw).

                    Soooo, if you have your pilot screws set at 1.5 (too lean for an SG) then you may be opening the throttle screw to maintain an idle which can cause more fuel from the main jets. (I think).

                    I found the best setting for the later carbs pilot screws as 2.5 turns out from a light seat and go from there.
                    Skids (Sid Hansen)

                    Down to one 1978 E. Stock air box with K&N filter, 81H pipes and carbs, 8500 feet elevation.

                    Comment


                    • #11
                      Originally posted by skids View Post
                      I was thinking the same thing Scott. No. 3 is by the throttle screw. 4 is synched to 3. 1 and 2 are synched to 3 (throttle screw).

                      Soooo, if you have your pilot screws set at 1.5 (too lean for an SG) then you may be opening the throttle screw to maintain an idle which can cause more fuel from the main jets. (I think).

                      I found the best setting for the later carbs pilot screws as 2.5 turns out from a light seat and go from there.
                      Yep, the transition/intermediate circuit is the major part of the pilot circuit.
                      The idle port with the mixture screw is branched off of the pilot circuit just ahead of that cluster of 3 transition/intermediate ports.
                      The only adjustments for the transition/intermediate circuits are the pilot fuel and air jets.

                      Turn on your handy-dandy box fan and point it at the engine, then enter the Vicious Circle:
                      Adjust the throttle plate screws.
                      Adjust the idle mixture screws.
                      Readjust the throttle plate screws.
                      Readjust the idle mixture screws... etc., etc., etc., etc. (/Yule Brenner)
                      -- Scott
                      _____

                      2004 ST1300A: No name... yet
                      1982 XJ1100J: "Baby" SS Brakes, '850 FD, ACCT
                      1980 XS1100G: "Columbo" SS Brakes, '850 FD, ACCT
                      1979 XS1100SF: "Bush" W.I.P.
                      1979 XS1100F: parts
                      2018 Heritage Softail Classic 117 FLHCS SE: "Nanuk" It's DEAD, it's not just resting. It is an EX cycle.

                      Comment


                      • #12
                        Scott is correct. The pilot jet controls four holes however the pilot screw only acts on the one at the throttle plate, the 3 behind it are fed at a constant rate from the pilot jet no matter what.

                        With that said, the fact cyls 1 and 2 are up to temperature does not mean 1.5 turns is necessarily bad. If it was a problem with the pilots setting 1 and 2 would would not be up to temperature. As 1 and 2 synchronize together, there definitely is something different going on between 3 and 4. Something is keeping #4 from getting fuel. Find that and you find your fix.

                        With respect to float height, as soon as you hit the first bump, go around a corner, accelerate or brake, the floats are not physically perfectly identical. No matter what you set them at on the bench nothing stays static in a dynamic situation on the road. Get them within manufacturer spec and be done with it. Chasing float height is not your issue, it's in the pilot circuit.
                        Last edited by Bonz; 05-09-2020, 10:16 PM.
                        Howard

                        ZRX1200

                        BTW, ZRX carbs have the same spacing as the XS11... http://www.xs11.com/forum/showthread.php?t=35462

                        Comment


                        • #13
                          Originally posted by thebottle View Post
                          Just checked, and the gauges read the same if I move them to the same cylinder.

                          When everything is 1.5 turns out, I can sync them but then #4 doesn't get fuel.

                          At 1.5 turns and the carbs "synced" I can turn the sync screw between #3 + #4 until #4 gets fuel, but then #3 gets cold, and the readings are waaay off on the gauges then.

                          Or at 1.5 turns with them again synced, I can turn the idle screw way out on #4 until it gets fuel, then resync them on that... but it doesn't seem like I should have to turn the idle screw that far out, right? So I'm leaning toward it being the pilot circuit on #4.

                          Tomorrow I'm going to clean #4 again, and re-bench sync them, and go another round with it. Really want this running correctly this weekend so I can start on the other stuff that needs fixing like the master brake cylinder and suspension and then it's finally back on the road! Can't wait!
                          Looks like you got it figured out and you're correct on the turns out on #4.
                          I've had good results on my carbs and the ones I've rebuilt for others by starting at 2 turns out on the pilots and going richer from there.
                          Seems like 1-2-3 are running a little lean by the high temps is why I suggest going a bit richer.
                          1980 XS1100G "Dolly G" Full Dresser (with a coat of many colors )
                          1979 XS1100SF (stock-euro mods planned)
                          1984 XV700L Virago (to be hot-modded)
                          1983 XJ750MK Midnight Maxim (semi-restored DD)
                          1977 XS650D ( patiently awaiting resto)

                          Sometimes it takes a whole tank of gas before you can think straight.

                          Comment


                          • #14
                            Could be a good point on the high temps on #1, #2, #3. I don't know what the temp difference would be from 1.5 turns to 2.0 or more. If there's a fan blowing on them my thought is the temp shouldn't be near 600 degrees when doing a sync. That is really hot! Thoughts?
                            Howard

                            ZRX1200

                            BTW, ZRX carbs have the same spacing as the XS11... http://www.xs11.com/forum/showthread.php?t=35462

                            Comment


                            • #15
                              Hehehe, "I was getting really good lean and mean mileage, then it got even better after I burned holes in the pistons and had to park the bike!"
                              -- Scott
                              _____

                              2004 ST1300A: No name... yet
                              1982 XJ1100J: "Baby" SS Brakes, '850 FD, ACCT
                              1980 XS1100G: "Columbo" SS Brakes, '850 FD, ACCT
                              1979 XS1100SF: "Bush" W.I.P.
                              1979 XS1100F: parts
                              2018 Heritage Softail Classic 117 FLHCS SE: "Nanuk" It's DEAD, it's not just resting. It is an EX cycle.

                              Comment

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