Most street-driven VW's will benefit from running a distributor that has both vacuum and mechanical advance features.  This type of distributor is known in the industry as being an “SVDA”, or Single Vacuum Dual Advance distributor.  A metered vacuum signal is created in the carburetor and sent to the distributor at partial throttle.  This results in improved efficiency of the engine.  At highway speeds, with this additional advance in timing, the engine requires less pedal travel to run at the same speed.  This results in better mileage.  As the pedal is cycled down more toward wide open throttle, this vacuum signal is dropped out so as to not create too much total advance, which would result in pinging and detonation.  An additional benefit of running this type of distributor is at slow speeds.  As the pedal is cycled from closed to open, a pulse of vacuum is sent to the distributor, which advances the timing.  This helps smooth out the dreaded “flat spot” associated with mechanical distributors.  This modification is not a “fix” for poor tuning, set-up, or jetting, but can really help make your car run better.

Unfortunately, the Kadron Solex H40/44EIS carburetors were never imported from the factory with this feature.  This service is included with every new set of carbs that have the “Kaddie Shack Magic” modifications package performed, and every set of our “Turn-Key” rebuilt and re-bushed sets.  

This modification is not a simple one, and should be professionally done to ensure proper vacuum signal at all levels of throttle position and RPM range.  Several passages are meticulously modified when we complete this service.  Some are reamed to a specific size, some are filled, and a fitting is pressed in to hook up your vacuum hose.  Vacuum caps are provided, so you can use the feature, or run a mechanical advance.  Only one carburetor is generally used to supply the  vacuum, but both can be teed in if a larger camshaft is used with more overlap.

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