The factory appears to be slowly phasing out the Flo-Jet series in favor of highly modified Walbro carburetors. Engines in the 9-to 13-cubic-in. range use variants of the small series Walbro, recognized by its angular appearance and removable air bleed jet, mounted just aft of the air cleaner. The removable main jet nozzle has been [...]
Small, medium, and large two-piece Flo-Jets are the only up-draft carburetors in the Briggs line. Figure 4-4A shows the parts layout common to all three models. Needle & seat Extract the elastomer seat by threading a self-tapping screw into the fuel orifice (Fig. 4-11). Press in a replacement seat—PN 230996 for gravity feed, PN 231019 [...]
Carburetors do not wear out in the accepted sense of the term. Most failures are associated with “soft” parts, such as inlet needles and seats, diaphragms, and gaskets. After long service, the throttle shaft bearings might develop enough play to justify replacement, when such repairs are possible. Light varnish deposits respond to lacquer thinner and [...]
Pulsa-Jet carburetors include a fuel pump, which is actuated by a vacuum diaphragm. Side-mounted diaphragms are discussed in an upcoming section titled “Vacu-Jet & Pulsa-Jet.” The tankmounted diaphragm (Fig. 4-10), used on one version of this carburetor, concerns us here. Figure 4-6 illustrates the places where vacuum leaks typically develop at the tank interface. Figure [...]
Most late-production Vacu- and Pulsa-Jet carburetors are equipped with a type of automatic choke unique to Briggs & Stratton. The choke valve is normally closed by a spring and pulled open by a manifold vacuum acting on a large diaphragm. The choke butterfly should snap closed when the engine stops and open as soon as [...]
The carburetor bolts to the engine block or makes a slip-fit connection, sealed by an O-ring, with the fuel-inlet pipe. The fuel supply must be shut off on gravity-fed systems, either with the valve provided or by inserting a plug into the carburetor end of the flexible fuel hose. Warning: Some gasoline will be spilled. [...]
Engines that operate under a constant-load regime might not have provision for idle. Once the engine starts, the governor raises engine speed to a preset rpm. This discussion applies to engines that left the factory with an idle capability and now refuse to exercise it. Check for air leaks at the carburetor mounting flange, cylinder-head [...]
Long bouts of cranking with the choke closed will flood any carburetor, wet the bore, and spill fuel out of the air horn. Two-piece Flo-Jets flood quite easily. Note: Carburetor flooding, characterized by fuel puddling in the bore, must be distinguished from external leaks. Fuel will cascade past a worn or twisted float-bowl gasket. Tank-mounted [...]
A blackened spark plug, acrid, smoky exhaust, and loss of power suggest an overly rich mixture. It is assumed that turning the mixture adjustment screws (when present) has no effect and that the air filter has been cleaned or, if made of paper, replaced. The choke butterfly opens fully, as verified by visual inspection with [...]
This fault will appear as loss of power, possible backfire as the throttle plate is suddenly opened, and a dead-white or bleached-brown spark-plug tip. The engine seems to run better when choked. Backing out the high-speed adjustment screw (when present) has no effect. Begin by looking for air leaks downstream of the throttle plate. Focus [...]
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