The Specifications of a Mikuni BS32SS Carburetor

by Tim McQuade

The Mikuni BS32SS was a 32-millimeter, constant-velocity carburetor. A CV carburetor creates a more fluid air flow travel than some other carburetor types, which results in maintaining proper mixture levels and better engine performance. Because of its efficient design, the BS32SS carburetor was used in the 1980s in a variety of vehicles and motorcycle brands, such as Suzuki and Yamaha.

Carburetor Measurements

The Mikuni BS32SS carburetor had a 1.3-inch bore size, with a standard idle rpm of 1,150, plus or minus 100 rpm. The fuel level measured at 0.2 inch, plus or minus 0.02 inch, and the float height measured 0.88 inch, plus or minus 0.04 inches. The main air jet measured 1.7 millimeters. The by-pass measured 0.8 millimeter and the pilot outlet measured 0.7 millimeter. The valve seat measured 2 millimeters. The recommended cable play for both the throttle cable and choke cable measured 0.5 to 1 millimeter, or 0.02 to 0.04 inches.

Designations and Carburetor Settings

In the Suzuki GS 700, the BS32SS used ID No. 06A00 in most E-03 models, while in California it was ID No. 06A10. In the Mikuni naming conventions, the main jet was #122.5 and the pilot jet was #37.5. The jet needle designation used in the Mikuni BS32SS was 5C-28 and the needle jet specification was Y-5. Mikuni used a starter jet identified as #45 and a throttle valve specified as #135. The pilot screw and pilot air jet came pre-set.

Emissions Control

The Mikuni carburetor was designed to meet the 1980 United States Federal Emission Regulations. Any motorcycle having over 50 cubic centimeters of engine displacement was required to adhere to this emissions level. This called for a hydrocarbon level no greater than 8 grams per mile and a carbon monoxide level no greater than 19.3 grams per mile. The main jet, needle jet and pilot jet were all components specifically calibrated to allow the Mikuni BS32SS to meet the required emission level requirements.

Carburetor Troubleshooting

According to Suzuki, if the air cleaner fails in the Mikuni BS32SS carburetor, it could be due to the presence of dirt or excess oil lubrication. A faulty fuel level in the carburetor could be caused by a sticking float, a leaking needle or an incorrect carburetor setting. A leaking or sticking linkage could cause the choke to malfunction. Clogged or restricted carburetor jets, a too lean or too rich float level, leaking choke plunger or sticking linkage, or air leaks in the intake manifolds or engine gaskets could all cause mixture malfunctions in the carburetion system.

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