These WT-668 carburetors have been custom modified with high quality rubber-sealed bearings on each side of the throttle shaft.
This mod helps with keeping sand and fine dust from entering via the shaft area via the weakest part, the carb shaft.
When it enters it can gum up the shaft so that it binds, sticks open and in turn wears the carb shaft so it creates an air leak.
This mod stops 99% of dust and sand from entering the carb making the carb basically maintenance free.
The carburetor is delivered, spring calibrated and pressure checked