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Vacuum Ports

The BS32 and BS34 Mikuni carburetor assembly for a Kawasaki motorcycle has four vacuum ports shown in the photo above.  On a motorcycle with original equipment, the two outside carburetor vacuum fittings (carburetors #1 and #4) will have hoses connected and joined with a tee fitting.  This tee will then be connected to a fresh air vacuum switch which in turn connects to fittings on the valve cover.  The #2 carburetor vacuum fitting is connected to a vacuum actuated petcock fitting located on the left underside of the gas tank.  The #3 carburetor vacuum fitting will be capped. If any vacuum fitting is not connected, it MUST have a vacuum cap else it creates a major air leak and the motorcycle's pistons WILL be damaged.  The assembly pictured has vacuum caps on all four vacuum fittings as it was tested on a motorcycle that didn't require their connection.  3/16"or 7/32" vinyl vacuum caps work best.  Don't use rubber caps as the rubber deteriorates and cracks quickly.  If 1/4" plugs are used, put a dab of super glue on the bottoms of the caps so they don't pop off when the bike is operated or use small hose clamps.  The vacuum fittings will be used when synchronizing the carburetor assembly.  Suzuki models do NOT have these fitting as the intake manifolds are equipped with vacuum fittings.


The small  fittings on the bottom of the bowls are drains.  BS series carburetors do not have overflow circuits.  A drain fitting allows gas to flow from the bowl when the drain screw is loosened.


There are vents on BS series carburetors.  Some types of BS assemblies use plastic venting tees located between the #1 and #2 carburetors and between the #3 and #4 carburetors.  If your carburetor assembly is so configured, you should connect overflow hoses to these vents and route the hoses over the swingarm.  In the event the motorcycle tips over, gas will come out these vents and you want to avoid gas from spilling onto a hot engine.  The other type of BS carburetor assembly venting is via holes cast into the edge of the intake-side venturi.  Since your airbox connecting runners or pods will cover these openings, nothing further should be done. The main thing is to NOT obstruct or block the bowl vents as the float assemblies rely on venting to function properly.
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