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What causes surging? SOLVED

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guido guzzi:
Hello All,
My carbureted 96 Sport 1100 just turned 33,000 miles and has started surging between 3800 and 4000 rpm. I know I should keep the revs over 4K but sometimes it cannot be helped.
Has the stock airbox and not planning to remove it. If it ever did this before it was not nearly as noticeable. Carbs are synched at idle and valves are correctly set to non-US specs (.006 and .008?).
IIRC there's no way to synch carbs at 4000 or so, right? First thought was an air leak creating a lean condition... Any insight appreciated.
John Wendt in Wisconsin

n3303j:
Sync carbs at idle with manometer and idle stop screws.
Sync carbs at 4K with nanometer and throttle cable tension adjuster.

Check for intake air leaks or slow fuel delivery.

Rebochi:
  A possible build up of fuel deposits on the emulsion tube and jets, easy to access and clean. Drop the float bowls and have a look.

guido guzzi:

--- Quote from: n3303j on June 05, 2023, 09:02:34 AM ---Sync carbs at idle with manometer and idle stop screws.
Sync carbs at 4K with nanometer and throttle cable tension adjuster.

Check for intake air leaks or slow fuel delivery.

--- End quote ---

Thank you for the input fellas.  :thumb:
n3303j , sync at 4K with throttle cable free play adjuster?

n3303j:

--- Quote from: guido guzzi on June 05, 2023, 09:21:53 AM ---Thank you for the input fellas.  :thumb:
n3303j , sync at 4K with throttle cable free play adjuster?

--- End quote ---
Not sure how your linkage is set up. But somewhere in there is something that will let you adjust tension on just one or the other carb cables. Systems aren't perfect so manufacturers install adjustment points so they don't have to be.
Make sure both cables have a bit of slack at idle position.

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