I would check the cable first, it sounds like it may not have seated corecly in the slide, within the carby.

Once you have assessed the cable seating, if the problem persists, make sure the idle screw (grey) is not set to high, and that the kill switch wires are inserted correctly.

Also make sure the throttle adjustment screw on the throttle box is not missing, causing the cable to slip.

Cheers
Ty

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