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  • #1

    Inconsistent Power

    I've got an '89 Hawk that I'm getting back into working condition. When I put it away in 2008, it was acting up the same way it is now. When I'm riding at a given throttle position, the engine will suddenly generate more power, then back off. The engine doesn't quit, it just goes between these high and low power states. It seems to happen around 4-5000 rpm.

    I don't think it's carb or fuel related due to the suddenness of the change.
    I don't think it's ignition related because the engine never quits generating power.

    Could it be a valve that sticks intermittently?

    Bike data:
    I'm the original owner.
    20,000 miles
    All stock, no mods

    -Jason
    Tags: None
    • #2
      If it's happening between a certain RPM, like 4k-5k, I would suspect the needle or carb slide. I'm assuming the carbs got a cleaning after pulling the bike back out for service. Although it is odd it did it before its hibernation.
      ASMA #139

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        • #3
          Originally Posted by Talon
          If it's happening between a certain RPM, like 4k-5k, I would suspect the needle or carb slide. I'm assuming the carbs got a cleaning after pulling the bike back out for service. Although it is odd it did it before its hibernation.
          Yes, I tore down the carb and cleaned it well.

          Would an intermittent spark plug cause this?

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            • #4
              Are the hoses that are supposed to vent to atmosphere on the carbs venting?
              Hawk with many differently shaped fuel tanks.

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                • #5
                  Originally Posted by Henway
                  Are the hoses that are supposed to vent to atmosphere on the carbs venting?
                  Interesting thought.


                  It's very likely carb related. Hawk ignition system won't usually fail intermittently, and ever rarer intermittent but consistent at the same rpm.

                  Sticky slide could do that.

                  Air leak is also a very viable option. Check for leaks around the bottom of the carbs where they enter the boots by spraying some carb clean or starter fluid at them and seeing if it revs up. If so, air leak
                  Don't spend money and buy, spend time and learn.

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                    • #6
                      STEP ONE: remove 3 sparkplugs for inspection and post a closeup photo here.

                      could be one cylinder firing inconsistently, so consider changing plugs, cleaning connections at coils and grounds. probably not carb, but as 6 sez the slide could be sticking. need to locate which cylinder has the problem.

                      guessing it could a be the CDI box going bad or pulse coil ? very rare failures, but........
                      Last edited by squirrelman; 01-11-2023, 09:36 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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                        • #7
                          Originally Posted by Talon
                          If it's happening between a certain RPM, like 4k-5k, I would suspect the needle or carb slide…
                          I once had a similar problem. Turned out the star lock nut that secures one of the needles had come unseated. Once locked into place, never again an issue…
                          This forum is entirely dedicated to wasting time and money modifying a slow motorcycle. - joel

                          Nothing like a project to keep you busy, slowly draining funds out of the wallet! - spacetiger

                          Our Hawks have all the power any mature, sensible rider can use on any street or highway without carrying around excessively unnecessary big-bore weight and power - squirrelman

                          Bike builds can be and most time are art and expression. To take something mass produced and impersonal and make something personal that you can't stop staring at as you walk away. There is nothing I find more satisfying than looking at something cool and beautiful and thinking "I made that". - 6
                            👍 3

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                            • #8
                              If it has always done it then it might be worth taking note of how you have it tuned. Are your jets stock as well? A lot of folks will say stock and then not realize jetting was changed without a needle change.
                              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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