Husqvarna Chainsaw Carburetor Repair Manual

The diagrams in this description do not correspond with the carburetor fitted on the chainsaws. They serve only to show the principles of design and operation.
Design
The carburetor consists of three sub-systems:
• Metering unit
• Mixing venturi
• Pump unit
The metering unit contains the jets and fuel control functions. It is here the correct amount of fuel for the given engine speed and power is metered.
The mixing venturi houses the choke, throttle valve and diffuser jets. Here air is mixed with the fuel to give a fuel/air mixture that can be ignited by the ignition spark.
In the pump unit, fuel is pumped from the fuel tank to the metering unit. One side of the pump diaphragm is connected to the crankcase and pulses in time with the pressure changes in the crankcase. The other side of the diaphragm pumps the fuel.
Operation
The carburetor operates differently in the following modes:
• Cold start
• Idling
• Part throttle
• Full throttle
In the cold start mode the choke valve is fully closed. This increases the vacuum in the carburetor and fuel is easier to suck from all the diffuser jets. The throttle valve is partly open.
In the idling mode the throttle valve is closed. Air is sucked in through an aperture in the throttle valve and a small amount of fuel is supplied through the diffuser jet.
In the part throttle mode the throttle valve is partially open. Fuel is supplied through the diffuser jets.
In the full throttle mode both valves are open and fuel is supplied through all three diffuser jets.
Dismantling
Dismantle all parts necessary and remove the carburetor from the saw. On some models the cylinder needs to be loosened and lifted to be able to remove the carburetor.
Plugs
When cleaning the carburetor the plugs must be removed. Remove as follows:
1. Drill a hole in the plug.
2. Insert a screwdriver or punch in the hole and prise up the plug.
Semi fixed jet and fixed jet
Some carburetors have an extra jet (semi fixed jet). The jet is of brass and is located in the metering unit and is used to give a fuel supplement. On average 10% of the fuel passes through the jet. Below or next to the jet is a screen which needs to be cleaned.
Dismantle the jet and/or screen in one of the following ways:
1. Knock the unit into the venturi using a punch and take the unit apart. (some Tillotson models).
2. Dismantle the lock washer over the jet and lift off the jet and screen.
Cleaning and Inspection
Clean all components in petrol. Wear gloves or skin protection cream.
WARNING!
Never direct the compressed air jet towards the body. Air can be forced into the blood stream and can cause fatality.
Use compressed air to dry the petrol on the components. Direct the air through all channels in the carburetor housing and ensure that they are not blocked.
Refer to the carburetor diagram in question on the previous pages and check the following:
1. That the gasket and pump and control diaphragms are undamaged.
2. That there is no play on the throttle and choke valve shafts.
3. That the needle valve and its lever are not worn.
4. That the fuel screen is undamaged
5. That the tips of the high and low speed jet screws are not damaged.
6. On Tillotson HS 255 B, that the speed governor is clean.
7. That the air intake manifold is not cracked.
Assembly
Plugs
1. Place the plug in the hole with the convex side facing upwards.
2. Expand the plug by using a punch on the top side.
Semi fixed jet and fixed jet
Reassemble the jet and/or screen in one of the following ways:
1. Put together the unit and fit it in the carburetor by means of a punch (Some Tillotson models).
2. Fit the jet with screen and lock washer.
Pressure testing
Pressure testing should be carried out with the carburetor fully assembled. Testing should always be carried out after the carburetor has been repaired, but a test can also be made for troubleshooting before dismantling.
Make the test as follows:
1. Set the high and low speed jet screws one turn open from the bottom.
2. Connect pressure tester 502 50 38-01 to the carburetor’s fuel intake.
3. Lower the carburetor into a beaker of water.
4. Pump up the pressure to 50 kPa (0.5 bar) and clamp the pump tube with the spring clip.
5. There should be no leakage. If a leakage occurs refer to the table below.
Refitting onto chainsaw
Fit the carburetor to the chain saw and refit any other parts removed.
For tightening torques, use Service data for the chainsaw in question.
Carburetor adjustment. See the operating instructions for the chainsaw in question.
Carburetors covered:
Tillotson HS 228 B
Tillotson HS 255 B
Tillotson HS 260 A
Walbro HDA and HD
Walbro WJ
Walbro WG
Walbro WT
ZAMA C1Q-EL1
#chainsawrepair #husqvarnachainsaw #husqvarna #husqvarnarepair #husqvarnacarburetor

[@barrett-small-engine-parts]

Order Husqvarna chainsaw carburetors at: www.amazon.com/s?k=Husqvarna+chainsaw+carburetor&crid=2GHNZZST49LKX&sprefix=husqvarna+chainsaw+carburetor%2Caps%2C263&linkCode=ll2&tag=barrett-small-engine-equipment-20&linkId=7a9a58ee489bf5f6002e76d711cbd03e&language=en_US&ref_=as_li_ss_tl (affiliate link - As an Amazon Associate we earn from qualifying purchases.)