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  • #1

    Plug reading

    OK, went for a ride yesterday, after warmed up backfiring a little while idling and alot when engine braking. Got home and read the plugs, 1,3,4 between a light brown to whitish grey. #2 was black as black gets. serious carbon build up. Carbs were synced with merc sticks last summer and haven't been touched since. SO I am thinking I need to adjust my idle mix screw on number 2. How many turns back in do you guys recommend? And I am assuming that this action will affect my carb sync, no? Floats are all set exactly to 25.8mm. reading in another post I beleive that 23 is stock? Hoever I dont think I need to adjust my float levels cause at WOT she screams all the way up the RPM scale.
    So is backfiring is caused by a lean condition ? It only does it when siting at idle and while engine braking.
    I am thinking I am gonna open up idle mix screws on 1,3,4 1/4 turn, and turn #2 in 1/2 turn or maybe 3/4. It was seriously carboned up. And then resync.
    Sound good?
    "Beware of any man that owns a pig farm"
    "Hence the meaning of the Saying,.. As greedy as a pig"
    79 XS1100 modified standard
    Chain Drive, Monoshock,extendend hand built swingarm, 200 rear
    pod filters,150 mains,45 pilots
    straight pipe 4-2 exhaust
    new to me 05 Kawasaki zxr12r man does she fly
    Owned 83 Honda V65 Magna
    Owned 02 Vstar 650 classic
    owned 85 Honda Shadow VT 700C
    Tags: None
  • #2
    Why resync? There might be a problem with the #3 slide not coming back down or with a float stiicking or something else. If it is a problem with the No. 2 pilot screw, the fouling would be caused at less than 3500 rpms for sure, and more likely, closer to idle rpms. I would turn the screw in a half turn, clean the plug and see what happens... (repeat as necessary)
    Skids (Sid Hansen)

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

    Comment

    • #3
      Backfiring or popping while decelerating or at idle can actually that rich #2 cylinder. Light brown or tan sounds like the others are pretty right. You need to inspect that carb to see why that one is running rich on its own. It may be something other than the carb. Then if you are truly sync'ed up then you should adjust the idle mix screws all at once. Screw in the idle mix screws UNTIL JUST SNUG and then open them all 1 1/4 turns. Start the motor and adjust them all one at a time by 1/4 turns waiting about 15 seconds for the adjustment to level out. Go in 1/4 turn until the motor begins to stumble then adjust back out and do this until you get the highest idle RPM. This should not affect your sync. but it is a good idea to check it again after you adjust.
      Mike Giroir
      79 XS-1100 Special

      Once you un-can a can of worms, the only way to re-can them is with a bigger can.

      Comment

      • #4
        Allright, some background. When I had the sync done (friend,and bike mechanic) I had been riding on the highway for about and hour to his shop at high RPMs. We pulled the plugs before the sync and they were white. So he said/did turned the mix screws out 1 1/2 more turns(keep in mid that I am running pod filters and open headers.) They were @ 1 1/4 before this. At this point I had 145 mains and 45 pilots. He said I should go up to 150 mains. Then we did the sync. Since then I have gone up to 150 mains.
        Right now, I think that 1,3,4 are good. maybe a little lean but I can deal with it atleast they are all really close to being the same.
        SO I really dont want to touch them. Can I use TADracers idea just for the #2 carb?
        Oh yeah TAD I dont know what this means
        "Backfiring or popping while decelerating or at idle can actually be that rich #2 cylinder" ??
        "Beware of any man that owns a pig farm"
        "Hence the meaning of the Saying,.. As greedy as a pig"
        79 XS1100 modified standard
        Chain Drive, Monoshock,extendend hand built swingarm, 200 rear
        pod filters,150 mains,45 pilots
        straight pipe 4-2 exhaust
        new to me 05 Kawasaki zxr12r man does she fly
        Owned 83 Honda V65 Magna
        Owned 02 Vstar 650 classic
        owned 85 Honda Shadow VT 700C

        Comment

        • #5
          Your exhaust gaskets may need replacing.

          I had the same (at least similar) problem and that fixed 95% of the popping. Is the popping coming from the mufflers? If the gaskets aren't sealing, then air is leaking in and allowing the unburned fuel to ignite. I don't know how running open headers would affect the situation.
          -Do what makes you happy.

          '79 Honda CB 750 K (2)
          '78 XS 11 E - "Rhona"
          ...and a 2nd E, for the goodies on it.

          Comment

          • #6
            Hold it.

            #2 has carbon build up? It's not lean, it's RICH. I'd bet you have a float problem or a needle seat problem in #2

            Comment

            • #7
              I thought a stuck float caused fuel in the airbox/fuel in the oil/crankcase. From my understanding of how these carbs work, a stuck float (open) shouldn't cause it to run rich, but just flood the airbox, or crancase. I guess I could see how it would make it run rich, if the bowl was so full it flooded the slide needle. I am pretty sure it is not the float. I just had the bowls off making sure all my floats were the same height and they move really well. It may be the needle seat. But wouldn't it show signs of flooding when not running?? IE the flooded airbox/crankcase. I really think I need to turn my idle mix screw back in some. But I will take all of your advice into consideration, and make the appropriate checks.
              BTW my #2 carb was formally known as a #4 CARB. had to modify it for the vacuum advance line.
              "Beware of any man that owns a pig farm"
              "Hence the meaning of the Saying,.. As greedy as a pig"
              79 XS1100 modified standard
              Chain Drive, Monoshock,extendend hand built swingarm, 200 rear
              pod filters,150 mains,45 pilots
              straight pipe 4-2 exhaust
              new to me 05 Kawasaki zxr12r man does she fly
              Owned 83 Honda V65 Magna
              Owned 02 Vstar 650 classic
              owned 85 Honda Shadow VT 700C

              Comment

              • #8
                To hell w/ reading plugs! This is my newest toy (yet to be installed).

                '81 XS1100 SH

                Melted to the ground during The Valley Fire

                Sep. 12th 2015

                RIP

                Comment

                • #9
                  I'd say to hell with carbs with you if I wasn't so damn poor!!
                  "Beware of any man that owns a pig farm"
                  "Hence the meaning of the Saying,.. As greedy as a pig"
                  79 XS1100 modified standard
                  Chain Drive, Monoshock,extendend hand built swingarm, 200 rear
                  pod filters,150 mains,45 pilots
                  straight pipe 4-2 exhaust
                  new to me 05 Kawasaki zxr12r man does she fly
                  Owned 83 Honda V65 Magna
                  Owned 02 Vstar 650 classic
                  owned 85 Honda Shadow VT 700C

                  Comment

                  • #10
                    81xsproject, explain that gadget, please.
                    1985 Yamaha VMX12n "Max X" - Stock
                    1982 Honda XL500r "Big Red" - Stump Puller. Unknown mileage.
                    1974-78 Honda XL350 hybrid - The thumper that revs. Unknown miles.
                    1974 Suzuki TC/TS125 hybrid. Trials with trail gear. Invaluable. Unknown miles.
                    1971 Honda CL350. For Dad. Newtronic Electronic Ign. Reliable. Unknown miles.

                    Formerly:
                    1982 XS650
                    1980 XS1100g
                    1979 XS1100sf
                    1978 XS1100e donor

                    Comment

                    • #11
                      I do believe that is part of his EFI project??
                      "Beware of any man that owns a pig farm"
                      "Hence the meaning of the Saying,.. As greedy as a pig"
                      79 XS1100 modified standard
                      Chain Drive, Monoshock,extendend hand built swingarm, 200 rear
                      pod filters,150 mains,45 pilots
                      straight pipe 4-2 exhaust
                      new to me 05 Kawasaki zxr12r man does she fly
                      Owned 83 Honda V65 Magna
                      Owned 02 Vstar 650 classic
                      owned 85 Honda Shadow VT 700C

                      Comment

                      • #12
                        Or uhhhhh part of his MSD project??
                        "Beware of any man that owns a pig farm"
                        "Hence the meaning of the Saying,.. As greedy as a pig"
                        79 XS1100 modified standard
                        Chain Drive, Monoshock,extendend hand built swingarm, 200 rear
                        pod filters,150 mains,45 pilots
                        straight pipe 4-2 exhaust
                        new to me 05 Kawasaki zxr12r man does she fly
                        Owned 83 Honda V65 Magna
                        Owned 02 Vstar 650 classic
                        owned 85 Honda Shadow VT 700C

                        Comment

                        • #13
                          But what does it need to be used on the XS? How is it connected? How much does it cost?
                          1985 Yamaha VMX12n "Max X" - Stock
                          1982 Honda XL500r "Big Red" - Stump Puller. Unknown mileage.
                          1974-78 Honda XL350 hybrid - The thumper that revs. Unknown miles.
                          1974 Suzuki TC/TS125 hybrid. Trials with trail gear. Invaluable. Unknown miles.
                          1971 Honda CL350. For Dad. Newtronic Electronic Ign. Reliable. Unknown miles.

                          Formerly:
                          1982 XS650
                          1980 XS1100g
                          1979 XS1100sf
                          1978 XS1100e donor

                          Comment

                          • #14
                            Or, what possible use could it serve?

                            Comment

                            • #15
                              Maybe its got four sensors that plug into the carb to head vacuum ports and take fuel mix ratio readings, to help him either 1) adjust his carbs, or 2) send info to the EFI control unit to adjust ratios. ????
                              Just my best uneducated guess though
                              "Beware of any man that owns a pig farm"
                              "Hence the meaning of the Saying,.. As greedy as a pig"
                              79 XS1100 modified standard
                              Chain Drive, Monoshock,extendend hand built swingarm, 200 rear
                              pod filters,150 mains,45 pilots
                              straight pipe 4-2 exhaust
                              new to me 05 Kawasaki zxr12r man does she fly
                              Owned 83 Honda V65 Magna
                              Owned 02 Vstar 650 classic
                              owned 85 Honda Shadow VT 700C

                              Comment

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