Lois Alice and Don Ross demonstrate how to inspect, clean, and pressure test Walbro diaphragm carburetors for optimal operation. The discussion covers essential fuel maintenance tips to prevent ethanol-related damage and ensures proper adjustment for both butterfly and rotary valve models.
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hi I'm Lois Alice program manager for
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walbro and I'm Don Ross lawn and garden
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business unit manager this video is
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intended to help you inspect in-service
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walbro diaphragm carburetors whether the
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butterfly or rotary valve models as you
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know down a lot of changes in our
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industry have affected carpet or service
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the introduction of ethanol into our
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fuels affects the carburetor operation
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and tamper resistant features limits the
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amount of adjustment and users can make
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to the carburetors today we're going to
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discuss these topics along with the
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inspection and service of diaphragm
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carburetors in this video a basic
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understanding of the carburetor function
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will be very handy for this video so
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let's start there
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the carburetor does three important
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tasks first fuels drawn from the gas
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tank into the carburetor second the fuel
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is metered to match the engines RPM and
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load requirements and finally the
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metered amount of fuel is mixed with air
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and delivered to the crankcase at the
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proper time and the engines operating
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cycle to control the flow of fuel and
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air into the engine the carburetor uses
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pressure created within the engines
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crankcase known as an impulse the
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movement of the piston creates two types
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of impulses a negative impulse or vacuum
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is created during the Pistons upward
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stroke while a positive impulse is
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generated by the Pistons downward motion
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these impulses are delivered to the
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carburetor through machine channels in a
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manifold or impulse fitting the channels
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or fittings lead to the fuel pump the
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carburetor throat contains the throttle
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valve and in some models the choke bell
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that's good louie but if I think I've
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got a carburetor problem where do I
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start
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Don whenever you have a carburetor of
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any type that seems to be malfunctioning
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you first want to eliminate any
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potential causes that are not directly
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related to the carburetor always use
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fresh fuel based on the engine
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manufacturers recommendation engine
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problems resulting from bad spark plugs
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a clogged muffler or low compression can
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also be misinterpreted as carburetor
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problems so be sure to include these
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areas in your initial engine inspection
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procedures then check the fuel tank vent
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and the fuel filter for obstructions
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debris in either area could easily cause
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a fuel delivery problem if the filter is
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dirty clean or replace it with an
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original walbro fuel filter if the tank
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and vent are clear disassemble and
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inspect the air filter because
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carburetors depend on an adequate
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airflow a clogged filter could result in
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an overly rich condition next check the
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fuel and primer lines be sure they
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aren't pinched plugged or cut your
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initial inspection should also include a
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pressure check of the fuel line and the
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carburetor pressure testing the
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carburetor reveals the operating
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condition of the inlet needle connect
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your walbro pressure tester part number
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57 - 11 to the fuel line apply air
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pressure by slowly depressing the
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plunger the gauge will indicate an
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increase in pressure until in the end
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let needle valve unseats
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this level is referred to as the Popoff
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pressure and may range from 15 to 50 psi
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due to the variety of carburetor design
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specifications occasionally the inlet
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needle valve will not on see in this
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case you'll need to disassemble the
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carburetor which we'll get into in just
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a bit
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after popping off the gauge will drop to
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indicate the pressure at which the inlet
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valves receipts this is referred to as
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the receipt pressure the inlet needle
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should reseat and hold a minimum of 5
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psi complete the pressure check by
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performing the same test at the
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carburetors fuel Inlet if pressure tests
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show proper needle operation
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it's time to check the carburetor
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mounting area and the manifold and
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gasket connecting the carburetor to the
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engines crank case for wear damage be
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sure to inspect the impulse passage
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leading to the fuel pump chamber
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crankcase impulses must be able to reach
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the carburetor for it to operate
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properly to test put a drop of oil over
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the passage crank the engine a few times
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and watch the oil if the oil doesn't
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move or only move slightly the passage
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is blocked it must be cleared
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if the engine you're working on has a
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reed valve check the valve it should be
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free of debris and properly aligned with
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the intake port we should note that
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everything we've talked about so far
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applies to all types of diaphragm
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carburetors but now we want to look
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specifically at servicing the two major
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types of walbro diaphragm carburetors
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that are used in handheld equipment
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walbro manufactures a variety of
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butterfly valve carburetor models yet
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their components are all very similar
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let's see how a butterfly valve
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carburetor functions the butterfly valve
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carburetor can be divided into three
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basic areas of operation the fuel pump
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the fuel metering area and the throttle
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and choke valve the fuel pump is made up
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of a cover a gasket a diaphragm and the
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pump side of the carburetor body the
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pump is activated by crankcase impulses
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delivered through a machine channel or
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an impulse fitting the metering side
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also includes a fuel Inlet screen the
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inlet needle orifice
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the inland needle and the fuel metering
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chamber the meter and chamber is made up
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of a cover a metering diaphragm a gasket
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a metering lever pin and spring and
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nozzle check valve and the idle assembly
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located within the carburetor body and
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the idle adjustment screw the final area
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of operation includes the choke and
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throttle valve assemblies the throttle
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valve assembly is made up of a shaft
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lever assembly spring and valve the
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choke is made up of a shaft and lever
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assembly choke friction ball spring and
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a valve the amount of fuel delivered in
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the crank case is determined by the
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position of the throttle valve the more
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open the valve the more airflow the more
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air flow the greater amount of fuel
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delivered to the crank case
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well Louie that's a lot of good
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information it is down because a basic
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understanding of the butterfly valve
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carburetors function will come in handy
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as we inspect it for proper operation so
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let's get started and get into the
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proper procedure for inspecting the
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butterfly valve carburetor
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before you begin inspecting the
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carburetor be sure the metering and fuel
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pump areas are completely disassembled
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idle progression holes have been
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machined into the carburetor body these
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passages are accessible through a welsh
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plug to remove the welsh plug use tool
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number 500 - 16 available in both the
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400 - 595 and 500 - 500 walbrook
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toolkits position the sharp end of the
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tool at a slight angle and tap the tool
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until it penetrates the welsh plug then
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apply light pressure to the handle until
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the plug pops out be careful not to
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contact or damage to carburetor body
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with the tool once the carburetor is
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disassembled clean the entire body and
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its covers use mineral spirits to avoid
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damage to carburetor parts and blow a
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drive with approximately 25 psi of
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compressed air be sure all holes and
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passages are clear
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on models with a check valve that has a
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nozzle feed hole you can verify the
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nozzle check valves operation with a
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small holes or fuel line position the
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holes our fuel line over the meter and
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chamber side of the nozzle then draw the
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nozzle check valve up against the
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retainer two or three times to ensure
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its operating properly do not use a
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metal tool to clear the nozzle now we
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can reassemble the carburetor beginning
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by installing the Welsh plug using tool
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number 500 - 15 align the welsh plug in
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position the tool on the dome part of
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the plug then tap the plug until it
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becomes flat it's important that the
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plug is flat so it doesn't interfere
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with the function of the metering
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diaphragm assembly moving in the past I
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remember using nail polish to seal the
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wall plugs the Istana is true however
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because of ethanol fuels we no longer
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use fingernail polish or any kind of
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sealing on the Welsh post we found that
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ethanol fuels can dissolve the seal and
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and create other problems now we can
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reassemble the inlet needle metering
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lever pin spring and lever pin screw
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next check the lever height adjustment
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with wall bros metering gage number 500
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- 13 position the gage across the
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carburetor body the gauge should just
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contact a metering lever without opening
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the needle valve if the lever is
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misaligned use a small screwdriver to
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keep the head of the inlet needle
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stationary at the same time slide
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another small screwdriver to lift or
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depress the metering lever arm until
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it's properly adjusted
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this would be a good time to check the
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function of the inlet needle with the
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metering cover and metering diaphragm
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assembly removed apply pressure to the
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fuel Inlet fitting and manually depress
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the metering lever to ensure that the
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inlet needle moves freely if it doesn't
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disassemble the metering system
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completely and carefully clean the parts
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walbro small parts cleaner part number
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500 - 520 will help you clean these
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parts
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carefully inspect the needle tip and the
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non-service will see for debris or
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damage before reassembly if you're
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working on an older carburetor with a
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circuit plate design inspect the circle
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plate and gasket for signs of damage or
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wear the holes in the circle plate
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should be free of any obstructions next
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replace the metering diaphragm and
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gaskets using original wall probe parts
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but we understand that the likelihood of
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damage to soft parts in the carburetor
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is greater with ethanol fuels right down
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while walbro continues developing
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advanced engineering materials that are
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highly resistant to ethanol ethanol
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fuels can affect soft parts like
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diaphragms fuel pumps and gaskets on all
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carburetors plus ethanol tracks moisture
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causing corrosion of the aluminum parts
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and moisture in the fuel also reduces
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its shelf life so how can we avoid
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problems first use the fuel recommended
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by the engine manufacturer second make
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sure it's fresh and finally run the fuel
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out of the equipment if it's going to be
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six weeks or more before you use it
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again great tips Louise thanks let's
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continue our butterfly valve carburetor
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inspection reassemble the fuel pump
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beginning with a new fuel Inlet screen
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fit the new screen into the screen
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pocket and press to the screen pocket
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step using walbro tool number 500 - 15
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the screen should completely contact the
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casting wall next reassemble the pump
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diaphragm gasket pump cover and cover
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screw if any of the carburetor
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components are damaged replace them with
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original walbro parts a generic exploded
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view and a list of all the carburetors
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specific parts can be found at Walker's
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website at wwlp.com before reinstalling
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pressure test the carburetor as we
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discussed in the initial inspection
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section to ensure it has been properly
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reassembled
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if the carburetor passes the pressure
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test it can now be reinstalled on the
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engine and check for proper adjustment
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the way I understand the carburetor
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adjustment procedures have changed to
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accommodate newer carburetors with
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tamper resistant features that's right
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due to environmental concerns since the
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mid-90s carburetors have come equipped
12:39
from the manufacturer with tamper
12:42
resistant features of various kinds
12:43
these features limit the amount of
12:46
adjustment available to consumers in
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order to maintain low emissions the
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tools techniques and specifications
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needed to adjust these carburetors are
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available to authorized dealers directly
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from the engine manufacturer however
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resale these tools to consumers carries
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heavy penalties on all carburetors
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tamper resistant or not you can still
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adjust the idle speed screw refer to the
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manufacturers recommendations for
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settings that covers the operation
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troubleshooting and adjustment of wall
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rope butterfly valve carburetors further
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servicing information and an ample
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supply of original replacement parts can
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be obtained at your wall Road
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distributor walbro manufacturers various
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versions of rotary valve carburetors
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will the carburetors differ somewhat
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design the components can still be
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grouped into three basic areas of
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operation the fuel pump the metering
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area and the throttle shaft assembly
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most of these carburetors also come
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equipped with their own primer let's
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take a closer look at the components
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that make up the rotary valve
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carburetors three functional areas and
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their attachments the first functional
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area includes the fuel pump found
14:00
beneath the primer pump assembly the
14:03
fuel pump is made up of a gasket a
14:05
diaphragm pump body assembly and the
14:10
pump side of the carburetor body
14:12
removing these components also reveals a
14:14
fuel Inlet screen and an inlet needle
14:17
orifice the carburetor body also
14:19
contains a channel which allows
14:21
crankcase impulses to enter the fuel
14:23
pump the metering area is made up of the
14:26
inlet needle seat the main nozzle check
14:30
valve a metering diaphragm assembly the
14:34
metering lever pin spring and the inlet
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needle the inlet needle is held in the
14:40
closed
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position by the force of the spring
14:42
against the lever some rotary valve
14:45
carburetors may contain a serviceable
14:47
main jet the final area of operation is
14:50
the throttle area the rotary throttle
14:53
barrel assembly includes the barrel
14:55
valve needle spring throttle ramp idle
15:01
screw bracket idle adjustment screw
15:04
swivel and throttle lever most of
15:07
Waldo's rotary valve carburetors come
15:09
equipped with a priming system these
15:11
systems are designed to purge the system
15:13
of air and assist the carburetor during
15:15
startup the primer is made up of the
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purge body assembly cover and primer
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bulb and a number L check valve that
15:23
controls the flow of fuel and air during
15:25
the priming operation depressing the
15:28
primer bulb opens the outlet check valve
15:30
allowing air and fuels to exit the ball
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as the ball returns to shape a vacuum is
15:36
created opening the fuel inlet valve
15:38
causing fuel to circulate throughout the
15:40
carburetors fuel circuit and into the
15:42
bulb under most circumstances the bulb
15:45
should only have to be depressed four to
15:47
five times to properly prime the system
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to inspect rotary valve carburetors
15:55
begin by performing an initial general
15:57
inspection of the areas surrounding the
15:59
carburetor including air filter muffler
16:03
spark plug fuel filter and fuel holes if
16:09
no problem is found the carburetor must
16:11
be disassembled as you disassemble the
16:14
carburetor note the order in position of
16:16
the components this will help you
16:18
correctly reassemble the carburetor
16:20
after it's been inspected start the
16:22
disassembly procedure at the primer pump
16:24
assembly just below the primary assembly
16:27
is the metering area which consists of a
16:29
metering diaphragm assembly a gasket and
16:32
the metering lever pin spring and inland
16:37
needle leave the inlet needle lever pin
16:41
and spring assembled within the pump
16:43
body assembly unless they require
16:45
replacement removing the fuel pump body
16:48
is also the first step in disassembly in
16:50
the fuel pump the fuel pump consists of
16:53
the body a diaphragm a pump gasket and
16:57
the fuel pump side of the carburetor the
17:00
pump body assembly contains a fuel Inlet
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screen and the inlet needle orifice the
17:05
fuel pump side of the carburetor body
17:07
also contains the main jet and its own
17:09
ring once the carburetor is completely
17:12
disassembled clean its metal components
17:14
using mineral spirits now that you
17:17
finish cleaning up components it's time
17:19
to reassemble the carburetor begin by
17:23
reassembling the main jet will ring and
17:25
main jet into the pump side of the body
17:27
install the fuel Inlet screen into the
17:29
fuel pump cover using tool number 500 -
17:32
15 the screen should be pressed to the
17:35
screen pocket step and fit flush with a
17:38
pocket wall reassemble the meter area
17:41
using original walbro parts
17:51
you
18:10
check the lever height adjustment with
18:13
wall bros meter engage number 513 and
18:16
adjust as needed you have the option of
18:19
replacing the entire fuel pump by the
18:20
assembly as a replacement unit this
18:23
simplifies replacement and eliminates
18:25
the need for the meter and lever height
18:27
adjustment now reassemble the fuel pump
18:30
body assembly to the pump side of the
18:32
carburetor body using a new gasket and
18:34
diaphragm the final area to inspect and
18:39
reassemble is the primer pump assembly
18:42
reassemble using the gasket diaphragm
18:45
purge body bulb and cover
18:51
if the primary pump valve doesn't seat
18:54
properly or the primer bulb doesn't
18:56
return to shape replace the entire
18:58
primer pump assembly once you have
19:01
completely reassembled the carburetor it
19:02
must be pressure tested again the
19:04
procedure is the same as we use in the
19:06
initial inspection and also for the
19:08
butterfly valve carburetors using your
19:10
wall probe pressure tester number 57 -
19:12
11 determine the valves Popoff and
19:15
reseed pressure settings be sure the
19:17
inlet needle valve is wet before you
19:19
pressure test it the gauge will indicate
19:22
an increase in pressure until the inlet
19:24
needle valve unseats the inlet needle
19:27
should unseat between 15 to 60 psi
19:30
depending upon the carburetors design
19:32
specifications this level is referred to
19:35
as the Popoff pressure the gauge will
19:38
then drop to indicate the pressure where
19:39
the inlet legal valve receipts this is
19:42
also referred to as the receipt pressure
19:44
the valve should receipt at a minimum of
19:47
5 psi if the carburetor passes the
19:50
pressure test that can be reinstalled on
19:53
the engine and check for proper
19:54
adjustment
19:58
as we discussed with butterfly-valve
20:00
carburetors carburetor adjustment
20:02
procedures are different now because
20:05
newer carburetors have tamper resistant
20:07
features that's right since the mid 90s
20:10
car breeders have come equipped from the
20:12
manufacturer with tamper resistant
20:14
features of various types these features
20:16
are designed to limit the amount of
20:18
adjustment possible by consumers if
20:21
you're an authorized dealer the tools
20:23
techniques and specifications necessary
20:25
to adjust these carburetors are
20:26
available from the engine manufacturer
20:29
however these cannot be solved consumers
20:31
without the risk of heavy fines on all
20:34
carburetors Tampa resistor or not you
20:37
can adjust the idle speed screw just
20:39
refer to the engine manufacturers
20:40
recommendations for these settings
20:44
congratulations
20:45
this concludes the operation repair and
20:48
adjustment of walbro rotary valve
20:50
carburetors for more information on
20:52
servicing walbro diaphragm carburetors
20:54
the location of your nearest authorized
20:56
walbro distributor and other information
20:59
about walbro and its products