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top speed 114mph, What the F&*(?

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  • top speed 114mph, What the F&*(?

    i have an engineering question...

    why can both of my 250cc bikes do 108mph

    and my 1100cc bike only runs 114?

    this make no sense to me.....
    If someone would kindly explain why a 1100cc machine falls flat on it face at
    114mph when if i swaped sprockets i could "go" faster on my 250.

    as a side note.. Yes, i'm planning the FD swap(XJ750 FD).

    I'm running a 79 xs11 special, Did i mess something up? Or is this true top speed for my machine?

    most bikes around 500cc can break 120, most bikes 650 and up can do 130 min. (bikes newer then 1983)

    what's the deal?
    1979 XS1100SF Special.78 E motor/carbs, Jardine 4-2 exhaust, XS Green coils, Corbin seat, S.S. Brake lines, Hard cases, Heated grips.

    2012 FJR1300 Gen 2. Heli bar risers, R-gaza crash bars, mccruise cruise control.

    (2)2008 WR250R. Because kids outgrew others.

    2007 Suzuki V-Strom 1000. (Just added 2024) pre-crashed.

    1975 Kawasaki S1 250. My first bike. Still have it. NO I'm not selling it!!

    Most bike problems are caused by a loose nut connecting the handlebars and the seat!!

  • #2
    One theory from the UK site,

    Re: Fuel Tank capacity.
    « Reply #29 on: Today at 07:58:30 AM »

    --------------------------------------------------------------------------------
    Unfortunately it's the way of the motor industry, they make the first off, a superb beast and then gradually detune and sanitise the machine for the crowd that couldn't hack the proper ones. They then, through clever marketing, convince the saddos (no offence) that what they are geting is better. Oh how easily people are fooled.

    Datsun did it with the Z series
    Honda did it with the CBX
    Yamaha did it with the XS11 (but went toooo far)

    .................................................. .................................................. ...

    or maybe it's just shagged and in need of a good overhaul.

    Comment


    • #3
      I would say you have some carb or exhaust issues if you only get 114. I had a cracked exhaust recently and had a top end of @ 118 per GPS. I fixed that and did nothing else and hit 126 without trying too hard.

      I don't remember the exact formula, but after you start pushing winds at a certain speed, you start needing exponentially more HP with equal wind drag. Something like a bike that does 140, needs nearly double the hp to do 150.. or something like that. BUT... a bigger motor will get you to that point much QUICKER... if we're talking 4 stroke motor versus 4 stroke.


      Tod
      Try your hardest to be the kind of person your dog thinks you are.

      You can live to be 100, as long as you give up everything that would make you want to live to be 100!

      Current bikes:
      '06 Suzuki DR650
      *'82 XJ1100 with the 1179 kit. "Mad Maxim"
      '82 XJ1100 Completely stock fixer-upper
      '82 XJ1100 Bagger fixer-upper
      '82 XJ1100 Motor/frame and lots of boxes of parts
      '82 XJ1100 Parts bike
      '81 XS1100 Special
      '81 YZ250
      '80 XS850 Special
      '80 XR100
      *Crashed/Totalled, still own

      Comment


      • #4
        If everything is in good mechanical shape such as cams timed well, good compression, adequate spark then it has to be tuneup related.

        A 79 special with the 16" rear wheel numerically should do 170 or so in 5th at the 8500 rpm redline but like trbig says, over 130 or so, power consumption vs speed gained becomes an issue and things will flatten out quickly. In my younger and wilder days I have been over 130 on mine several times but it took some careful tuning to get there.
        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


        • #5
          A 79 special with the 16" rear wheel numerically should do 170
          I'm assuming a typo here... that should read 140.


          Tod
          Try your hardest to be the kind of person your dog thinks you are.

          You can live to be 100, as long as you give up everything that would make you want to live to be 100!

          Current bikes:
          '06 Suzuki DR650
          *'82 XJ1100 with the 1179 kit. "Mad Maxim"
          '82 XJ1100 Completely stock fixer-upper
          '82 XJ1100 Bagger fixer-upper
          '82 XJ1100 Motor/frame and lots of boxes of parts
          '82 XJ1100 Parts bike
          '81 XS1100 Special
          '81 YZ250
          '80 XS850 Special
          '80 XR100
          *Crashed/Totalled, still own

          Comment


          • #6
            lol
            That's what I figured too...
            I've done 125 with more throttle to go... but if I thought the XS could do 170... I wouldn't have much need for the FJ...
            81 SH Something Special
            81 frame, 80 tank and side covers, 79 tail light and carbs, 78 engine, 750 final drive mod, Geezer rec/reg, 140 mains, LH wheels


            79 SF MEAUQABEAUXS
            81SH Nor'eas tah (Old Red)
            80 LG Black Magic
            78 E Standard Practice


            James 3:17

            If I can make at least one person smile, or pee their pants a little, or maybe spit out their drink; then my day is not wasted.

            “Alis Volat Propriis”

            Yamaha XS 1100 Classic
            For those on FB

            Comment


            • #7
              Your XS is most likely not putting all the power to the ground that it could

              I've hit 125, and at the rate it was going 135 would have happened about 3 seconds later....darn highway patrol...

              Comment


              • #8
                Originally posted by danteinien View Post
                Your XS is most likely not putting all the power to the ground that it could

                I've hit 125, and at the rate it was going 135 would have happened about 3 seconds later....darn highway patrol...
                Better the highway patrol slowing you down than a guardrail.

                Don
                currently own;
                1980 Yamaha XS1100 SG
                2009 Yamaha Star Raider

                Comment


                • #9
                  I have had the XJ and XS in the mid 120's and was still accelerating. Both bikes were pretty much stock.
                  Harry

                  The voices in my head are giving me the silent treatment.

                  '79 Standard
                  '82 XJ1100
                  '84 FJ1100


                  Acta Non Verba

                  Comment


                  • #10
                    Originally posted by DJinNH View Post
                    Better the highway patrol slowing you down than a guardrail.

                    Don
                    I think we all need reminding of that once in a while (maybe just me?). Last night the nice officer reminded me. Seems every time I step out of line they are their to remind me that I should be "fill in lecture here". I guess I picked the wrong time/area to check top end... Back to reality now, no more stupid shazit, gotta stop and think before following that dumb idea…
                    I did shake the guys hand and thanked him for being kind.
                    '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


                    • #11
                      I haven't run the stock FD for quite a while, but if I am really pulling, I am still in fourth at 115.

                      If you want the speed, make sure you keep it wrapped up. If you shift and it goes under about 5k, you're not going to win that battle.
                      Ich habe dich nicht gefragt.

                      Comment


                      • #12
                        A lot of it comes down to the engineering in both bikes.

                        An XS1100 is about 95hp, in perfect tune, but wieghs 630lbs.

                        A 2006 cr250 dirt bike is 59hp @ 212lbs.

                        The difference is the xs can sustain the high speed all day, whereas the dirt bike would not last very long at full speed on a highway.
                        Nice day, if it doesn't rain...

                        '05 ST1300
                        '83 502/502 Monte Carlo for sale/trade

                        Comment


                        • #13
                          I think you need to get into that motor some. My 80g hardbagger w/full Windjammer has tagged 117 on the speedo with two up and it was still pulling. A observed 121 was hit riding solo before the killer wobble set in. So that being said, and the other testements to high triple diget speeds, ya might wanna start with the basics. Pull the plugs and read em, that will give you some indication how the carbs are working. First thing I would do would be a compression check to see how healthy the basic motor is. Trying to tune a tired engine can be pretty much fruitless. Aerodynamics play a big part when you start clearing a 100mph but even the upright position of a special should net you a higher top end than 114. As mentioned before, you need to keep the motor wound up pretty tight in 3rd, 4th and keep it twisted tight in 5th. Fuel flow was also mentioned, if there ain't nuff gas flowing, its not gonna go very fast and may "seem" like its running right.
                          When a 10 isn't enough, get a 11. 80g Hardbagger

                          Comment


                          • #14
                            Top speed is all about total power; gearing really doesn't enter into it (unless the vehicle will redline in top gear) as long as you're reasonably close to the torque peak at maximum speed. Most vehicles will 'calculate' out to a much higher top speed than they can actually attain. As an example, my XJS Jag was advertised as having a 160 mph top speed, but this was at 5K rpm. Redline on the motor is 6500 and the calculated top speed is over 190.

                            With that said, you're definitely down on power, as any XS11 should be able to break 120 with ease. For what it's worth, I saw 141 indicated on my '78 (just once! honest!) when it was fairly new.

                            And a guy I know who runs at Bonneville told me that for every 10% increase in speed, you need 30% more HP, so the numbers get pretty big pretty fast.

                            '78E original owner
                            Fast, Cheap, Reliable... Pick any two

                            '78E original owner - resto project
                            '78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
                            '82 XJ rebuild project
                            '80SG restified, red SOLD
                            '79F parts...
                            '81H more parts...

                            Other current bikes:
                            '93 XL1200 Anniversary Sportster 85RWHP
                            '86 XL883/1200 Chopper
                            '82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
                            Cage: '13 Mustang GT/CS with a few 'custom' touches
                            Yep, can't leave nuthin' alone...

                            Comment


                            • #15
                              you have to turn the throttle all the way...
                              " She'll make point five past lightspeed. She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself. "

                              79 xs11 standard
                              xs pods, Kerker 4-1, zrx1200r carbs mikesxs coils 35k voltz of power!!!
                              8mm msd wires
                              tkat fork brace...
                              Fox shocks...
                              mikes650 front fender
                              led's gallore...
                              renthal bars
                              gold valve emulators
                              vmax tensioner
                              Rifle fairing

                              Comment

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