Adjusting the Carb on a Briggs and Stratton 8 hp
The Briggs and Stratton 8 horsepower (HP) engine uses a horizontal shaft output. The carburetor is a Flo-jet type that suctions gasoline into an air mixture chamber from the lower float bowl. Gasoline is regulated into the float bowl from the fuel tank by a brass float. There are two adjustment valves on the Flo-jet carburetor, the needle valve and the idle valve. The needle valve regulates the amount of gasoline pulled into the mixing chamber for high-speed operation, while the idle valve regulates fuel for lower speed operation.
List:
Fresh gasoline
Slot screwdriver
Fill the fuel tank half-full with fresh gasoline. Ensure the fuel filter is clean and free of any foreign obstructions. Improper fuel flow to the float bowl reservoir inhibits the carburetor adjustment.
Turn the needle valve and idle valve in a clockwise direction to seat the valves close with the screwdriver. Do not over tighten as damage will result to the seats. Open the lower needle valve 1 1/2 revolutions in a counterclockwise direction. Turn the idle valve 3/4 of a full revolution in the same direction.
Start the engine according to the manufacturer's operational instructions. Some devices may require mechanical levers to be placed in neutral positions for starting.
Allow the engine to reach operational temperatures, generally 3 to 4 minutes.
Move the acceleration lever to full speed. Turn the needle valve in a clockwise direction until the engine begins to loose speed. Back the needle valve slowly in the opposite direction, counterclockwise, until the engine runs smooth.
Reduce the speed of the engine by lowering the acceleration lever to the idle position. If the engine stops, open the idle screw a 1/4 turn in a counterclockwise direction. Start the engine. Move the acceleration lever from high speed to idle several times. Adjust the idle valve until the engine no longer dies when speed is reduced.
Operate the engine under a full load condition. Make minor adjustments to the carburetor if needed.
Words to the Wise:
The needle valve is located on the lower left hand side of the round float bowl. Some models use a thumbscrew while other's have a slot type screw. The idle valve is located on the right hand topside of the carburetor. It is strictly a slot type screw head.
If the engine operates erratically after the above adjustment, inspect and replace the sparkplug. The sparkplug may have become fouled from improper adjustment and operation to the engine.
