The needle's "seat" could very well be the problem, but I would also check the mechanical functionality of the float and/or float lever, as well as the float level adjustment, i.e. (float height) If the "float height" is set high, it means that the floats actually sit lower in the carburetor bowl when upright - allowing the needle's seat to block off the main fuel passage when there is sufficient fuel in the bottom of the bowl to supply the motor, and when that fuel level gets too low, the float simply lowers with the level of the fuel and allows more to pour in, pretty simple in-fact. Now on the other hand, if the "float height" is set low, the floats sit higher in the bowl, requiring more fuel to rise the floats up and shut the main supply off. The problem begins when they are set "too low" and the amount of fuel required to rise the floats at the shut off point is greater than the amount it takes to "over-flow," hence the name "Overflow tubes." For more information, including proper float height adjustment, refer to the Cylmers manual if they are stock carburetors or the manufacturer's website. Hope this helps.