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    Carb Balance?

    I have an 1989 hawk 650 that I have brought back to life. Love it. Yoshimura slip on muffler, factory pro jet kit. Had the carb’s professionally cleaned and rebuilt. They look perfect. Followed instructions of factory pro jet kit from Hord. Engine would idle, but fell on its face given any throttle. My experience with jet kits is they are always too rich, at least where I live. I am three miles from the Pacific Ocean in far Northern California (Humboldt County). Sea level, cool air and high humidity. After going down, down, down with the jet sizes- 150f 142r small improvement. Replaced ridiculously rich needles with stock ones. Started up and ran great! Lean plugs though. Needles now shimmed 2.0mm, jets at 150 front, 160 rear. Rear still too lean!
    new carb boots installed correctly. Vacuum membranes look good. The vacuum slides have a needle holder unlike what is shown in the stock parts schematics found online. The needle holder screws in and then there is a screw on top to hold the needle in. I could move the needle up and down so I took the small spring from the needle holder found online and cut it real short to hold the needle in place. All passages in carbs unrestricted, although I’ll check that again. Replaced port seals in carb spigots. Fuel screws 2.5 out. Where is your favorite place to ride? pilots.
    My suspicion is the carbs are no synchronized. Visually the butterflies open exactly together. Can’t find a factory sync vacuum gauge to buy. I have found little on this site referring to synchronization.
    Your thoughts?
    Thanks in advance,
    Bruce Braly

    #2
    If you can't find a carb synchronization gauge on Amazon or similar, you could try this:

    https://www.superhawkforum.com/forum...nometer-26916/

    Carb synch'ing is described page 3-8 in the service manual.

    Comment


      #3
      bad carb synch is most noticeable at idle speed and up to about 3000 rpm, not above. reading your post, i don't think synch is any part of your problem. the needle holder you describe seems like a rare HRC part, and 2mm washers is way more than normal, better to relocate clip. are both vacuum slides identical or different ? before messing with washer adjustments, the main jets need to be selected first for best top speed.

      have you verified that float height settings are correct ?

      nov3-21 015.jpg
      (note that carbs must be held at a certain angle for measurement)


      do both slides move up equally with throttle increase (engine running and top of airbox and filter removed for test).

      what evidence shows the rear is running lean ?
      Last edited by squirrelman; 05-15-2022, 02:40 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.

      Comment


        #4
        Carb synch won't be responsible for something that sounds that dramatic. Something else is going on.

        If they were terribly out of balance it would barely idle and it would sound like the cylinders are fighting each other.

        You can always pull them and do a bench synch that will get them close enough to eliminate that as a possibility. I sometimes don't even bother hooking up my gages after a bench synch when it starts and idles perfectly smooth.
        Last edited by Captain 80s; 05-15-2022, 03:07 PM.
        "I couldn't afford NOT to buy it!"

        Comment


          #5
          Everyone else already said it.. but if visually they open together, look somewhere else for your issue.
          Don't spend money and buy, spend time and learn.

          Comment


            #6
            And man. I live at sea level and the factory jet kit needles are absolutely great.

            Id take another look at your jetting. Starting with the assumption that the kit is too rich may not be the best plan.

            Also if you are having a plug that looks real lean with a 160 jet and the other looks good on a 150 is look for air leaks on that cylinder.

            Do you have new intake boots on it, or old? How are your clamps. Are they old, and do they have that stupid spacer still? If so yank that out.
            Don't spend money and buy, spend time and learn.

            Comment


              #7
              No mention yet of what's in front of the carbs.

              Individual filters or the stock air box?

              Also... moving this from how-tos to mechanical and technical.

              If you were looking for a support group you're barking up the wrong tree. This place is fulla enablers dude. - Shooter77us

              The bitterness of low quality lingers long after the thrill of a low price has gone. - RacerX450

              Comment


                #8
                You need stock slides for the Factory Pro jet kit, not the RC30 "HRC" slides.
                J.D. Hord
                Keeper of Engine Nomenclature, 9th Order

                Comment


                  #9
                  Originally Posted by Hordpower View Post
                  You need stock slides for the Factory Pro jet kit, not the RC30 "HRC" slides.
                  Didn't even know that was a thing..

                  Learn something new every day.

                  Listen J.D. you I'm sure have plenty of free time and nothing going on that's important...

                  But.... You need to do a brain dump. "R.C. 31, The Book. By J.D. Hord"


                  Just let it all out.. release that knowledge into the world. I feel it would be a good thing and won't take much time at all.




                  But for real... You are the man with the knowledge and no one is coming behind to catch up and pass it on. A book I feel is the solution.
                  Don't spend money and buy, spend time and learn.

                  Comment


                    #10
                    Thanks for all your reply’s. Definitely not carb synchronization. It’s good. I’ll definitely get the proper vacuum slides. Thanks for catching that. What I think is happening is the rear vacuum slide is not lifting as much as the front one. Then I can try the factory jet kit needles and I bet that will fix it, unless it doesn’t! I love a mystery.
                    Bruce

                    Comment


                      #11
                      Originally Posted by 6 View Post

                      Didn't even know that was a thing..

                      Learn something new every day.

                      Listen J.D. you I'm sure have plenty of free time and nothing going on that's important...

                      But.... You need to do a brain dump. "R.C. 31, The Book. By J.D. Hord"


                      Just let it all out.. release that knowledge into the world. I feel it would be a good thing and won't take much time at all.




                      But for real... You are the man with the knowledge and no one is coming behind to catch up and pass it on. A book I feel is the solution.
                      People sometimes ask when I make a recommendation on jetting how I came to the numbers and I just say it's what JD told me to set up for on my own junk and I leave it at that.
                      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

                      Comment


                        #12
                        Vacuum slides are NLA. The only ones I have seen are Chinese copies on ebay.
                        Brian - Richland, WA
                        1991 Hawk GT
                        1997 VFR

                        Comment


                          #13
                          The "HRC" slides that TBR sold back in the day were just RC30 slides... (aside: there was nothing "HRC" for the Hawk, do you really think HRC would make race parts for the Hawk, LOL) and they didn't work worth a shit. I have absolutely no idea what the point of it was, other than they had the cool needle hold downs with screws. Maybe for their race bike, but for street bikes... no. And Factory needles are based on the stock slides.

                          If one slide is laggy, then there's your real problem.
                          J.D. Hord
                          Keeper of Engine Nomenclature, 9th Order

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