mixture screw question

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  • 650mark
    XStremely XSive
    • Jul 2012
    • 307
    • Mesa, Az.

    #1

    mixture screw question

    I had my '80 special in the shop 8 months ago for valve adjust and carb adjust/synch. they removed (for the very first time since new) the factory original aluminum(?) plugs covering the mixture screws and when the tech was done he put some clear rtv into the holes covering the screws again. bike has run like a new one ever since but I noticed today that one of the rtv "plugs" was loose so I just pushed it back into its hole. are these "plugs" needed for proper carb function? any problems if they were not there? thanks
  • IanDMacDonald
    XS-XJ Super Guru
    • Oct 2010
    • 3917
    • Grand Blanc & Fenton, MI

    #2
    While the remote possibility exists that something could leak into the hole, the reason for those aluminum caps were to prevent riders from messing with the factory settings. If u notice in the manual, it says not to mess with them. I guess Yamaha never figured that we'd be knowledgeable to learn proper stoichiometric mixtures.
    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.

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    • FJ111200
      XStremely XSive
      • Oct 2007
      • 317
      • Crewe, Cheshire, UK

      #3
      Originally posted by IanDMacDonald
      stoichiometric.
      That's a big word.

      Comment

      • motoman
        Master of XSology
        • Aug 2005
        • 8413
        • Grand Junction, Colorado

        #4
        Originally posted by IanDMacDonald
        While the remote possibility exists that something could leak into the hole, the reason for those aluminum caps were to prevent riders from messing with the factory settings. If u notice in the manual, it says not to mess with them. I guess Yamaha never figured that we'd be knowledgeable to learn proper stoichiometric mixtures.
        .......and back in the day, dealers had the tin replacements after doing a sync to further discourage the curious.
        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

        • 650mark
          XStremely XSive
          • Jul 2012
          • 307
          • Mesa, Az.

          #5
          I think it's Japanese for "please leave it the hell alone". but I could be wrong

          however, it doesn't answer my question. if those plugs are not there will the air/fuel mixture be effected?

          Comment

          • hamjam
            XS-XJ Guru
            • Jul 2002
            • 1003
            • Toronto ontario Canada

            #6
            no it won't
            Seamus ร“ hUrmholtaigh
            Niimi Moozhwaagan

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            Comment

            • donebysunday
              XS-XJ Guru
              • Oct 2012
              • 1737
              • New Berlin, Wi.

              #7
              Originally posted by IanDMacDonald
              While the remote possibility exists that something could leak into the hole, the reason for those aluminum caps were to prevent riders from messing with the factory settings. If u notice in the manual, it says not to mess with them. I guess Yamaha never figured that we'd be knowledgeable to learn proper stoichiometric mixtures.
              They were there on 1 of my bikes ( before I found out what to do ) to waste fuel. Had to keep the enrichener full open for 2 mi. and then another 2 mi. on half. So by the time I hit the slab 4 mi. down the road from home the bike was ready to rock, BOUGHT NEW ! Never had a bit of trouble other than this so I guess the jetting was rich enough to keep from holing a piston.
              76 XS650 C ROADSTER
              80 XS650 G Special II
              https://ibb.co/album/icbGgF
              80 XS 1100 SG
              81 XS 1100LH/SH DARKHORSE
              https://tinyurl.com/k6nzvtw
              AKA; Don'e, UD, Unca Don'e

              Comment

              • DGXSER
                Doctor of XSology(Deceased)
                • Nov 2008
                • 12001
                • Cincinnati, Ohio

                #8
                They run fine without them. Only issue I ever had was when one of my springs on that screw was loose, one of my mixture screws apparently vibrated loose, and out, while at XSEast last year. Not something easy to see and diagnose. Also not something you pick up at o-Reillys or Autozone.

                But I have never put them in any carbs I have worked on.
                Life is what happens while your planning everything else!

                When your work speaks for itself, don't interrupt.

                81 XS1100 Special - Humpty Dumpty
                80 XS1100 Special - Project Resurrection


                Previously owned
                93 GSX600F
                80 XS1100 Special - Ruby
                81 XS1100 Special
                81 CB750 C
                80 CB750 C
                78 XS750

                Comment

                • Tat2demon
                  XSive Maximus
                  • Jun 2012
                  • 718
                  • Sioux Falls, South Dakota

                  #9
                  I put a small dab on mine to keep them from vibrating loose. Doubt they would but a little spot of rtv is cheap insurance.
                  Nate

                  78 XS11 "Matilda" 2H7 000364

                  2001 Raptor ACCT, T.C. Fuse Box, TC Bros Forward Controls
                  Kuryakyn Iso Grips/Throttleboss/Bar End Mirror, Custom Covered Seat
                  Shinko 712s, HID Headlight, RC Performance Exhaust
                  Bikemaster Daytona Handlebars, Galfer SS Brake Lines
                  Barnett HD Clutch Springs, T.C. Spin On Filter Adapter
                  K+N Air Filter

                  88 Voyager XII
                  81 XJ650 Maxim

                  Comment

                  • WMarshy
                    XS-XJ Guru
                    • Apr 2009
                    • 2402
                    • Mexico NY

                    #10
                    Originally posted by 650mark
                    I had my '80 special in the shop 8 months ago for valve adjust and carb adjust/synch. they removed (for the very first time since new) the factory original aluminum(?) plugs covering the mixture screws and when the tech was done he put some clear rtv into the holes covering the screws again. bike has run like a new one ever since but I noticed today that one of the rtv "plugs" was loose so I just pushed it back into its hole. are these "plugs" needed for proper carb function? any problems if they were not there? thanks
                    He could have done it for one of these 3 reasons or all...
                    1. So the screws dont back out and hold their setting
                    2. So no air or water leaks in
                    3. Keep the owner out

                    Since they have an o-ring #2 isnt a problem, I'd dare say it was primarily #3. Should'a asked him.

                    It's not a bad idea, eliminates one possible variable if you start having issues with the bike. I'd do it to mine if I had the later carbs...
                    Last edited by WMarshy; 06-17-2013, 04:26 AM.
                    '79 XS11 F
                    Stock except K&N

                    '79 XS11 SF
                    Stock, no title.

                    '84 Chevy K-10 "Big Blue"
                    GM 350, Muncie SM465, NP208, GM 10 Bolt with 3.42gears turnin 31x10.5 Baja Claws

                    "What they do have is an implacable, unrelenting presence and movement that bespeaks massive power lurking behind paint and chrome. They don't wail like a screeching ninja, the don't rumble like a harley. They just growl like a spactic, stressed out badger waiting to rip your face off and eat your soul." Trainzz~RIP~

                    Comment

                    • DGXSER
                      Doctor of XSology(Deceased)
                      • Nov 2008
                      • 12001
                      • Cincinnati, Ohio

                      #11
                      I think the reason for it is more likely to keep dirt and crap out. I have had to drill out at least one pilot jets, or mixture screw on about every single set of carbs I have had to work on. On the later model carbs, you never have issues getting those mixture screws out. But the later model carbs you get dirt and water in there and it tends to make then sieze up.
                      Life is what happens while your planning everything else!

                      When your work speaks for itself, don't interrupt.

                      81 XS1100 Special - Humpty Dumpty
                      80 XS1100 Special - Project Resurrection


                      Previously owned
                      93 GSX600F
                      80 XS1100 Special - Ruby
                      81 XS1100 Special
                      81 CB750 C
                      80 CB750 C
                      78 XS750

                      Comment

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