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    carb slides don't lift

    New to me Hawk idles and runs lower speeds very well, but open the throttle and nothing happens...I am familiar with basic CV carb functions...I balanced the carbs with an air flow meter, pod filters, vacuum chamber vents run to a still air location between the cylinders. With filters off,bike stationary, rev the engine hard and slides don't lift at all. Diaphragms show no damage, and are seated properly . Slides move up and down by hand but return slowly..There is a small tube in the vacuum chamber that must receive vacuum to lift the slides, they appear to be blocked, cant probe it with a brass wire strand, spray or compressed air.....Got any ideas? thanks...

    #2
    Anytime I have had an issue with the slides not lifting and the diaphragms were in good working it came down to me not seating the diaphragms properly. Even though I have done it dozens of times, it is still easy to get wrong. I always check by blowing air into the tubes that lead to the sub air filter.
    ASMA #139

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      #3
      talon is 100% correct that getting slide diaphragms seated properly is difficult now, as our rubber bits have shrunk and changed dimensions after all these years. my recommendation now is to NOT remove slide caps unless really necessary to replace the slide needle. very little dirt accumulates under the cap, so removal isn't really helpful.

      i've been doing intensive carb repair work for the last 6 weeks (mostly VFR and Hawk and yamaha radian, carbs sent to me for repair from internet forums) and found alot of problems with shrunken diaphragms being quite reluctant to seat in their grooves, and i finally have had to resort to gasket "stickum" to hold the rubber in the grooves while i carefully slide the top cap in place. it doesn't always work, and i've had to go back in to get the damn things seated right as many as 5 times before success.

      sept 5, 2021 007.JPG sept 5, 2021 020.JPG 8-21-21 new camera 029.JPG 12-1-17_176.JPG.855a0e6828772e377747193f47761e4d.JPG july 16 2021 019.JPG july 4 2021 012.JPG 8-25=2021 013.JPG


      in every case, correct fitment must be checked by blowing lung air into the 1/2" diameter black tubes next to the vacuum chambers to see that the slides rise smartly.

      ************************************************** ********************************

      >>>>>>> my advice to OP is to test diaphragms by the airblow method since he claims they are in good condition, but i don't think they're seated correctly and to forget about the idea of a blocked tube.
      Last edited by squirrelman; 09-11-2021, 05:04 PM.
      "It's only getting worse."


      MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

      Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

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        #4
        Best to sit them by pushing them down making them look like and umbrella. Get them to sit in the Grove add the spring and install the cap.
        Don't spend money and buy, spend time and learn.

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          #5
          Originally Posted by 6 View Post
          Best to sit them by pushing them down making them look like and umbrella. Get them to sit in the Grove add the spring and install the cap.
          that usta work b4 the rubber shrank, but not so easy now.
          "It's only getting worse."


          MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

          Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

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            #6
            Like 6 said, I make the umbrella shape then I simply hold a finger in the throat to keep the slide from going all the way down removing the umbrella shape. Easy to see that the loop lines up then too. I put the top on while still holding it up and put 2 screw across from each other. Has worked every time.
            Bill,
            88 Blue Hawk (bike #39), 89 Red Hawk, 2021 Rebel 1100 (bike 41) Some Past/sold in reverse order:,FZ09,97 Magna #1&2 , 97 VFR750F, 87 VFR400R, 88 Hawk, 86 SRX 600, 77 RD400, 79 CB650, 04 VFR, 88 Blue Hawk, 89 Red Hawk, Yamaha SRX600, Harley 1200C, Yamaha RD400, Harley 883R, Yamaha 750 triple, Vlx600, Honda 450, Honda 400, CB550F, Kawasaki H1, BMW R69US, Yamaha R5C 350, Honda 160, Bridgestone 175, 1950 Harley 74 w/sidecar, 65 Harley 250 Sprint, 1948 Harley and my 1st bike-1941 Harley 74 knucklehead my dad gave in1963.

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              #7
              Yup, blew air in and the slides, didn't lift...A bit of Vasoline to hold the diaphragm in place... all good now... can't thank you guys enough for the help!!!
              It's a nice piece to ride on the rural roads where I live...Now I can go faster and scatter the wildlife...

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                #8
                Originally Posted by squirrelman View Post

                that usta work b4 the rubber shrank, but not so easy now.
                You do more carbs than I dou friend, but I've been lucky. Have yet to have a set I can't seat.
                Don't spend money and buy, spend time and learn.

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                  #9
                  Squirrel, the JBM replacement diaphragms are worth it to not have to fight getting them seated in the top of the carb and having them all shrunk and shriveled. Can't help with other replacement parts but the JBM parts may lend to not having to replace a slide itself fwiw. Sometimes you can just clean the slide with some emery or 1500 grit sand paper and then put the JBM parts on and they work great.
                  88 Blue Hawk GT - Under construction but rideable (guest approved)
                  89 BlackHawk 2.0 - On the lift and being assembled
                  90 Hawk GT (color as to yet be determined) - Still on the shelf in crates

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