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Thread: Carb Flat Spot

  1. #1
    Senior Member Phill's Avatar
    Join Date
    Jul 2007
    Livingston (Scotland)

    Carb Flat Spot

    I have been running my car with the electric choke disconnected for some time now and it's running great. The butterfly valve doesn't fully open though as a result. I would say its 80% open and only opens 100% (i.e. 90 degrees) when the automatic choke is hooked up. However this results in a flat spot below 2000 rpm and slow pick up. At higher revs it's fine. The only way to rid the flat spot is to leave the choke disconnected. Logic tells me that the flat spot must be a result of too much air getting in but I can't find any air leaks anymore. I would appreciate any advice from the collective genius that is Euro-Nova?
    "The most beautiful kit car in the world - Motor"

  2. #2
    ***Euro-Nova Supporter*** Spacenut's Avatar
    Join Date
    Jul 2007
    Hampshire, UK
    Hi Phill - I would look at it another way. If the engine is leaning out at low speeds it may need more fuel rather than less air. Leaving the choke flap at 80% is reducing the air flow, not the fuel, which is governed by fixed jets in the main (depending on the type of carburettor).

    If your idle jets are clear of debris (it can happen, ask me how I know), then it suggests to me that maybe you could go up a size or two. Alternatively if you have an idle mixture screw you can wind it out a half turn or two and see what difference that makes.

    Sorry it has been a long time since I looked at a VW carburettor

    only Pythagoras can save me now!

  3. #3
    Senior Member Brett's Avatar
    Join Date
    Nov 2018
    Las Vegas,NV USA
    could be the ignition timing advance curve is wrong

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