Aprilia revs not dropping to tick over (idle)

Discussion in 'The Workshop' started by mattvick, Jun 22, 2017.

  1. mattvick

    mattvick New Member

    Messages:
    2
    I'm new here so Hello to everyone :)

    I have an 2004 Aprilia 125 Mojito Custom. When I stop at a junction the revs fail to drop down to tick over but remain close to the bite point of the clutch with the bike twitching a little as if it were eager to get going again. This happens often, but not always.

    I've stripped down the carburettor a couple of times and noticed that the black coating on the diaphragm piston is warn and flaking off in places. I've cleaned this, as best I can, and all the other carburettor parts with petrol and put back together but the problem persists. In the picture below you can see only a small amount of the black coating remains on the piston on the left (image found on the web but similar to my piston).

    [​IMG]

    Is the diaphragm piston the likely cause of the revs not dropping? Should I replace it or try and get a replacement carburettor? I've seen diaphragm pistons for about £45 on eBay. Could there be something else causing this and what should I check? Also should I buy some proper carb cleaner to clan the carb parts?

    FYI the idle screw was adjusted when the engine was warm.
     
  2. Tamiyacowboy

    Tamiyacowboy Pippa's Owner

    Messages:
    1,850
    Rides:
    Piaggio Skipper
    get bike warm again , then tickle the idle screw to see if rpm drops down , 9-10 times its the idle screw that just needs a slight tickle to help. also when you input tad of throttle dont roll of the throttle let it go so its snaps back, sometimes the snap back from the throttle is enough to let the idle setting lower than norm due to heat expansion and wear/tightness in cable sheathing
     
  3. mattvick

    mattvick New Member

    Messages:
    2
    Thanks Tamiyacowboy :) I'll try that and let you know if it solves it
     

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