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  • #1

    Carb Adjustment Issue?

    This is sort of a long story so I'll get right to it. I was having trouble with my SF, I try to start he regularly even if I cant go for a spin. I apparently waited too long. She would start right up as usual but die if I tried to throttle up. I called a local Yamaha dealer to get a recommendation of a mechanic. To my surprise they offered to work on her if I supplied any parts needed. And so they did, they cleaned the carbs, said my gas was green. no parts needed. So I go over to pick her up and though better than before, she ran like crap. I told them to try again AND I gave them instructions on how to sync the carbs.
    so back I go, pop the choke out 1 click and fired her up, straight to 4k rpm, I pushed the choke back in and she dropped to around 12-15 hundred but missed and popped for a while. she seemed to smooth out as she warmed up but still something's not right. Also when I throttled up and released she took a while to get back down to idle. The mechanic came out and we talked and decided (he suggested) that we try new plugs, he said when he looked at them they were black. I went with it as they hadn't been replaced in a good while but I don't think they're the problem. I'm thinking she's running too rich
    what do you guys think?
    "Do the right thing, even if nobody's looking"

    SR500E Black
    XS750SF Carmine Red
    XS1100SF Mustang Red Metalic
    (Bob worked on this one)
    Tags: None
  • #2
    Get a new mechanic

    I'd say it's a combination of too many unknowns. Were the carbs cleaned properly? (that's my first hunch) Second, does he even know how to properly tune the air/fuel mixture? Third, does he know how to properly sync the carbs to the #3? Voltage at your coils? Last time the valve lash was set?
    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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    • #3
      we can rule out, valve lash, it had been running fine before I let it set to long. I believe he sync'd the carbs correctly because I gave him the directions in writing. He claimed to have really cleaned them...twice Voltage at the coils is good. I'm thinking the air/fuel mixture might be the culprit. Do we have a step by step in writing somewhere on the site?
      "Do the right thing, even if nobody's looking"

      SR500E Black
      XS750SF Carmine Red
      XS1100SF Mustang Red Metalic
      (Bob worked on this one)

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      • #4
        Yes there is one, but DO NOT TAKE IT TO THE "MECHANIC"!! The bike is probably older than he is, and most "younger" mechanics can't fix anything, let alone diagnose a problem.
        You need to find the time to do the repairs yourself, or find a member here who lives close to you to help. I'm lucky in that I have two mechanics who are still working part time, and have worked on bikes like ours for years. They both are independent shop owners. With my 50 years of working on carbs, I've only run across one set that I just could not tune.
        Ray Matteis
        KE6NHG
        XS1100 E '78 (winter project)
        XS1100 SF Bob Jones worked on it!

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        • #5
          clean the carbs and tank

          Howdy,,,sounds like the gas went bad from just sitting....run a can of seafoam or techron and check your gas filters too, replace if junk is in them. Take it for a spin with the gas cleaner and hope the old gas sediment dissolves and it purrs like it should. As it was running decent before all this, it sounds like fuel sitting around, especially the new 10percent alcohol fuel caused some carb issues......try it and keep us informed...........Mike in Sun Diego
          mike
          1982 xj1100 maxim
          1981 venture bagger
          1999 Kawi Nomad 1500 greenie
          1959 wife

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          • #6
            Well Ray, There just aren't enough hours in the day right now And, if I can learn this guy something we have a shot at carrying on the information through another generation. I'd guess he's about 35 and he's interested, that's worth a lot to me anyway. Once us old guys start gumming our oatmeal, somebody has to carry on, right?
            "Do the right thing, even if nobody's looking"

            SR500E Black
            XS750SF Carmine Red
            XS1100SF Mustang Red Metalic
            (Bob worked on this one)

            Comment

            • #7
              Originally posted by Mstaab View Post
              Well Ray, There just aren't enough hours in the day right now And, if I can learn this guy something we have a shot at carrying on the information through another generation. I'd guess he's about 35 and he's interested, that's worth a lot to me anyway. Once us old guys start gumming our oatmeal, somebody has to carry on, right?
              Yes, and that be you, not some young non-knowledgable shop mechanic.
              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.

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              • #8
                HAHA, OK, I haven't been considered a young guy in quite a while, thanks!
                "Do the right thing, even if nobody's looking"

                SR500E Black
                XS750SF Carmine Red
                XS1100SF Mustang Red Metalic
                (Bob worked on this one)

                Comment

                • #9
                  Were the pilot jets changed? (I know you said "no parts") The K&L pilot jets are the wrong size in their kits, and I had the same symptoms until I got the right pilot jets.

                  Otherwise, seems like rich idle mixture. Were they set by counting turns? how many turns?
                  -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

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                  • #10
                    Mstaab, have to agree with Radioguy. Pilot jets HAVE to be Genuine Mikuni or it'll never run correct. Setting them with bike idleing and using lean-drop method is only correct way of setting fuel mixtures....back out substantially, start in till slight change is heard...then back out 1/8th and no more than a 1/4 turn. Do next three the same and may have to re-adjust idle down to 1100rpm as you go. Then of course, re-sync using a manometer or multiple vacuum gauges.
                    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.

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