Disassembly, Cleaning and Repair of Briggs and Stratton / Nikki Carb

Transcription

1 Disassembly, Cleaning and Repair of Briggs and Stratton / Nikki Carb #1 'Nikki' and the Briggs and Stratton logo are cast into the body (#1, white). Fuel enters the carb via the inlet pipe (#1, green) which may be straight or bent at a number of orientations. The idle fuel mixture screw, when present, is fitted with a limiter cap (#1, blue) to prevent overly rich or lean adjustments. A welch plug covers the idle fuel mixing well (#1, yellow). #2 Applications which use a primer have a fitting added to the side of the carb to which the primer tube is attached (#2, blue) on the same side as the fuel inlet pipe (#2, green). - Page 1 -

2 #3 The anti-afterfire solenoid (#3) screws into the bottom of the fuel bowl. When the engine is shut down the spark is disabled and the engine coasts to a stop. While the engine is coasting, fuel is still being drawn in from the carb, and the unburned fuel continues out to the hot muffler where it may explode loudly. The anti-afterfire solenoid stops fuel flow into the engine as soon as the keyswitch is turned off. The plunger or pintle is extended by a spring and retracts when supplied with 12 volts DC. As the fuel level rises in the bowl, the float pushes the inlet needle up against the seat thus metering fuel flow into the bowl. Some inlet needles may have a spring plunger to provide finer control of the fuel level. The float should sit parallel to the carb body when the inlet needle just makes contact with the seat. #4 To remove the float pull the hinge pin out by the flattened end, if it has one (#4, blue). Some versions of this carb have a spring (#4, white) that presses the fuel transfer tube body against the gasket and carb body. The main fuel jet is at the bottom of the fuel transfer tube (#4, red). - Page 2 -

3 #5 The inlet needle hooks into the float (#5) so that as the float rises and falls, it will push and pull the needle. The float hinge pin may be flattened on one end and can be pulled out in one direction only. The inset shows a plastic inlet needle that has a spring loaded plunger and a rubber tip (#5). Check the rubber tip of the inlet needle for wear, corrosion or damage, and that the plunger operates freely. #6 The inlet seat is molded as a part of the fuel transfer tube body (#6, red). The main jet is removable. It sits at the bottom of the fuel transfer tube and is slid in from the top. - Page 3 -

4 #7 On some versions of this carb the outline of the bowl gasket is molded into the fuel transfer tube body and they require an additional o-ring at the fuel inlet hole (#7, blue). The bottom of the carb body is machined flat (#7, inset). The main fuel path is at #7, red); the low speed fuel path is at #7, yellow. #8 The main jet can be removed by pushing it out the top of the fuel transfer tube. An o-ring provides a good fit (#8). - Page 4

5 #9 With the main fuel jet removed the idle fuel pickup port is visible. A wire indicates its location (#9). All fuel passes through the main fuel jet. The main and low speed fuel then flow up separate tubes in the fuel transfer tube body. #10 On this version of the carb the outline of the bowl gasket is cast into the carb body and the mating surface of the fuel transfer tube body is flat. The emulsion tube (#10, blue) extends into the main fuel transfer tube. Air from the main air bleed surrounds the emulsion tube and enters through a number of holes along its length. The fuel/air mixture then flows to the main nozzle. Fuel arrives at the inlet (#10, green). The low speed jet is at #10, yellow. - Page 5 -

6 #11 A mix of fuel and air from the emulsion tube exits through the main nozzle (#11, blue) into the venturi airstream. The inset shows a nozzle from a snowthrower application. #12 Air from the main air bleed (#12, green) enters the main fuel transfer tube and mixes with fuel in the emulsion tube on the way to the main nozzle. Air from the low speed air bleed (#12, yellow) mixes with fuel that has entered the low speed jet. A larger passage provides an atmospheric vent to the fuel bowl (#12, blue). - Page 6 -

7 #13 #14 Applications of this carb that use a primer for easier cold starts have a plug with a small orifice (#13) in the bowl vent path. Fuel from the idle fuel transfer tube passes into the idle jet (#14) which is a tiny hole in a brass insert in the carb body. #15 Air from the low speed air bleed and fuel from the low speed jet mix and arrive at the mixing well covered by a welch plug (#15, blue). - Page 7 -

8 #16 A fuel air mixture from the low speed mixing well is metered by the adjusting screw (#16) before entering the intake air stream. The limiter cap can be pried or pulled off with moderate force and the screw removed for cleaning. The preliminary setting for the screw is 1-1/4 turns out from lightly seated. #17 The low speed fuel discharge ports are inside the carb bore. The primary port (#17, yellow) is metered by the adjusting screw and delivers fuel when the throttle is near the closed position. The secondary port(s) deliver(s) increasingly more fuel as the throttle plate opens. The inset shows the low speed ports of a single-speed application with no low speed mixture needle. #18 Some versions have a choke return spring (#18, white). The inset shows the dust seal and spring. - Page 8 -

9 #19 The idle speed adjusting screw (#19) limits how far toward closed the throttle plate may travel. - Page 8 -