| 摘要 |
A carburetor for a scavenged two-stroke internal combustion engine has an enriched fuel-and-air mixing passage extending through a housing of the carburetor. Engaged to the housing is a body of an air flow modular assembly which carries a primary air flow passage which houses a butterfly-type control valve therein. The throttle valve of the fuel-and-air mixing passage is mechanically linked or cammed to the control valve of the air flow passage so that opening of the throttle valve soon after opens the control valve allowing additional air to enter and provide a leaner fuel-and-air ratio in the combustion chamber of the engine when running under load. The air flow modular assembly has a sealing-and-bearing assembly which eliminates air leakage from the surrounding environment along the shaft of the control valve and into the primary air flow passage. The sealing-and-bearing assembly has a bushing which inserts into a counter bore of a cylindrical bore which receives the rotating shaft of the control valve. The bushing is thereby disposed radially and sealingly between the shaft and the body of the modular assembly to journal the shaft and prevent air leakage. To prevent air bypass leakage around the plate of the control valve within the air flow passage, the bushing and respective counter bore do not extend all the way through the body and into the air passage, instead, a cylindrical sealing surface which in-part defines the cylindrical bore, sealingly engages the shaft axially between the counter bore and the air flow passage. In this way, the plate and body interface at the location of the rotating shaft can more exactly follow the contour of the air flow passage, thereby preventing unwanted bypass air flow when the control valve is closed.
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