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Thread: Knocking?

  1. #1
    apriliaforum Junkie seacuke's Avatar
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    Aug 2003
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    Knocking?

    Hi Y'all. Been a long time.

    I tuned my bike (2002 Capo) up this spring and have been happily riding for about 2 months this year. It's been a rough 5 years for me & 2 wheels, but I am finally getting back to it.

    The bike has been performing near flawlessly (aside from the occasional stutter between 3k & 4k RPM which I chalk up to Oxygen sensor issues & stock mapping), but on Wednesday something happened which has me nervous. I was in town running from errand to errand, and had been off the bike for about 20 minutes. Started it up fine, pulled out into a stopped traffic queue at a light. While idling, the engine "popped" 3 times. Twice in less than a second followed by 1 more about a second later. The frame shuddered with each pop, and it sounded mechanically "bad" - uncomfortable. In my untrained mind, I thought "it's knocking!"

    I rode it home uneventfully, and commuted one more day on the bike like normal. However, the knocking/popping/whatever it is has happened several more times, while cruising. I feel like I should stress that: when I'm revving on the throttle pushing the engine it's smooth like silk. When I'm cruising along with the engine at a steady pace (or idling) is when this happens. I feel it in my boots when it happens; the whole bike sort of loses that sweet rhythm of operation it normally has.

    I read a bit on knocking, and it seems like it's a situation that happens under acceleration. This is definitely not under acceleration; it's when the throttle is barely (if at all) twisted.

    I'm not super comfortable riding the bike until I figure out what this is. Should I just replace the crank position sensor and give it a twirl?
    -- Seacuke

  2. #2
    apriliaforum expert
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    Check your vacuum tubes 1st, if any are cracked and letting air in will give you similar issue (Tubes under the airbox)
    I'd rather have a full bottle in front of me than a full frontal lobotomy

  3. #3
    apriliaforum Member skvrnsk's Avatar
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    I got such knocking after swapping fried ECU with another one from a different gen Capo. And it was horrifying sound just as you described it.
    I thought the valves met the piston since I was messing with shims at the time, but turned out it was an ECU from the start. Changing map for the right one solved the problem.
    Something with ignition was messed up.

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