Husqvarna 435, 435E and 440E chainsaw carburetor adjustment, removal and refitting guide will help with any carburetor cleaning, replacement, inspection and correct running of the chainsaw. A Service Manual detailing the Carburetor removal and refitting procedures with full diagrams, as well as more complete chainsaw repair information, is available to download. Also a Husqvarna and 435, 435e and 440e Parts List, Operator Manual, and Zama carburetor manual are also available to view or download as a PDF which can be read on any device or easily printed.

Carburetor for Husqvarna Chainsaw 435, 435E and 440E

Fig 22

These show the principle for the design and function of the carburetor.

Design

The carburetor is based on three sub-systems:

• • The metering unit, A.
  • The mixing venturi, B.
  • The pump unit, C.

The jets and the fuel’s control functions are located in the metering unit (A). Here the correct quantity of fuel is adjusted for the actual speed and power output (see figure 22).

Fig 23

The mixing venturi (B) houses the choke, throttle valve, and diffuser jets. Here the air is mixed with the fuel to give a fuel/air mixture that can be ignited by the ignition spark (see figure 23).

In the pump unit (C), 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 (see figure 24).

Fig 24

Function

Fig 25

The carburettor operates differently in the following modes:

• Cold start mode
• Idling mode
• Part throttle mode
• Full throttle mode

In the cold start mode (see figure) the choke valve

(H) is fully closed. This increases the vacuum in the carburettor so that fuel is sucked more easily from all the diffuser jets (D, E, and F). The throttle valve (I) is partly open. Extra air inlet (J) is closed (see figure 25).

Fig 26

In the idling mode (see figure) the throttle valve (I and J) is closed and the choke valve (H) is open.

Air is sucked in through an aperture in the throttle valve and a small amount of fuel is supplied through the diffuser jet (D) (see figure 26).

In the part throttle mode (see figure below) the throttle valve (I) is partially open and the choke valve

Fig 27

1. is open. Fuel is supplied through the diffuser jets (D and E). The throttle valve (J) starts to open (see figure 27).

In full throttle mode (see figure below) all valves are open and fuel is supplied through all diffuser jets (D, E, F, and G). Extra air inlet (J) is also fully opened (see figure 28).

Fig 28

Dismantling the carburetor

Fig 29

• 1. Dismantle the cylinder cover and the air filter.
  2. Disassemble the handle holder (see figure 29).
  3. Push the throttle actuator rod out of the handle part. Unhook it from the carburettor (see figure 30).

Fig 30

• 1. Remove the return hose (B) and suction hose (C). Loosen the fuel pump (D). Let the fuel hose (G) remain in place (see figure 31).

Fig 31

NOTE!

Take care when lifting out the carburetor so that the fuel hose does not become loose.

• 1. Loosen the screws (E) and unhook the rubber mountings (F) (see figure 32).

Fig 32

• 1. Disassemble the pump cover (G) over the measuring chamber cover (R) and carefully remove the control diaphragm (H) with gasket (J).

Fig 33

• 1. Unscrew the screw (K) and remove the needle valve (L) with the lever (M), shaft (N) and spring (P).
  2. Unscrew the screw (Q) above the pump unit and carefully remove the gasket (S) and diaphragm (T).
  3. Use a needle or similar device and carefully pull up the fuel screen (U).
  4. Unscrew the high (V) and low jet screws (W) (see figure 34).
  5. If necessary, dismount the throttle valve (X), choke valve (Z) and air shutter (Y) and remove the shafts with levers and springs (see

figure 34).

Cleaning and inspection

Clean all units in clean petrol.

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. Check the following:

• • 1. That gaskets, pump, and control diaphragms are undamaged.
    2. That there is no play on the throttle and choke valve shafts.
    3. That the needle valve (L) and its lever (M) are not worn (see figure 33).
    4. That the fuel screen (U) is whole and clean (see figure 33).
    5. That the tips of the high (V) and low jet screws

(W) are not damaged (see figure 34).

• • 1. That the intake manifold (R2) is undamaged (see figure 33).
    2. The carburetor has an extra air shutter connected in parallel with the ordinary throttle valve.

Fig 34

Assembly

Fig 35

Maintain a high level of cleanliness when assembling the carburetor. The slightest contamination can result in running problems.

1. If the throttle and choke valves, together with levers and springs were removed, they should be refitted. The spring is tensioned 1-2 turns. Lubricate the shaft bearings with light oil.
2. Fit the high (V) and low (W) speed needles and springs. Note! Do not fully tighten the screws. This will damage the seats and needle tips.
3. Fit the fuel filter (U) by using the handle of a small screwdriver. (see figure 33)
4. Fit pump cover (G), gasket (S) and measuring chamber cover (R) over the pump unit (see figure 33).
5. Fit the needle valve (L) with the lever (M), shaft (N) and spring (P) and tighten the screw (K). Fit the expansion washer (F) (see figure 35).

Fig 36

1. Check using a ruler or the like that the lever is level with the assembly plane on the cover. The lever arm can be bent if necessary (see figure 36).
2. Fit the control diaphragm (T) with gasket (S) and measuring chamber cover (R) over the metering unit (see figure 37).

Fig 37

1. Press in the screen (U). Fit the measuring chamber cover (R) and tighten the screw (Q) (see figure 37).
2. Put together the gasket (J) and control diaphragm (H) and press up (see figure 37).
3. Assemble all the parts and tighten the four screws (see figure 37).

11.. Carry out a pressure test.

Pressure testing the carburetor

Fig 38

Pressure testing should be carried out with the carburetor fully assembled. Testing should always be carried out after the carburetor has been repaired, but it can also be carried out as troubleshooting before dismantling the carburettor.

See figure and carry out the test as follows:

1

Set the high and low jet screws two turns from the bottom.

2

Connect pressure tester to the carburettor’s fuel intake.

3

Lower the carburettor into a beaker of water (see figure 37).

4

Pump the pressure up to 50 kPa.

5

No leakage is permitted. If a leakage occurs refer to the table below.

Leakage at	Fault with
Diffuser jets Leakage in impulse tube Ventilation hole on the metering unit.	Needle valve Pump diaphragm Control diaphragm

Assemble on the saw

Fig 39

1. Press the carburettor down towards the partition wall. Make sure that it gets into the correct position.
2. Fit the filter holder by hooking the choke control into the choke lever (A).
3. Hook on the rubber mountings. Insert and tighten the screws.
4. Insert the return hose (B) into its position in the filter holder.

Fig 40

1. Press on the fuel diaphragm (D). Fit the suction hose (C) and return hose (B).
2. Hook in the throttle actuator rod into the carburetor. Thread the handle holder into the throttle actuator rod (A). Push the rod forwards so that it can be inserted into the handle part.

Fig 41

1. Push down the handle holder into the filter holder (see figure 42).
2. Assemble the air filter and cylinder cover.

Fig 42

1. Mount the handle holder.

Carburettor adjustment Conditions during adjustment

Fig 43

• • The air filter should be clean and the cylinder cover fitted when adjustments are made. Adjusting the carburettor with a dirty air filter will give a too lean fuel mixture the next time the air filter is cleaned. This can result in serious damage to the engine.
  • Mount, for this model, approved bar and chain combination (see Technical data in the Operator’s Manual).

435/e 16″

440e 16″

• • The chain should not be tensioned more than that it remains ~ 0,2 inches to the bar.

(See figure 43)

Fig 44

Replacement of the H-needle or complete carburetor

1. Carefully screw the new H-needle to the bottom and turn it anticlockwise ”A” turns.

435/e A = 2

440e A = 2

1. Start the engine. If necessary, adjust the idling speed with the T-screw until the chain stops.
2. Adjust the H-needle to give a top speed of ”B” rpm. Use a tachometer.

435/e B = 12500 -13 000, speed limitation 440e B = 12500-13 000, speed limitation

Use screwdriver 530 03 55-60.

1. Let the engine run at ”B” rpm ~ 1 minute, until warm.

Replacement of the L-needle

1. Screw the new L-needle to the bottom and then turn it counterclockwise ”D” turns.

435/e D = 2,5

440e D = 2,5

(See figure 44)

Husqvarna 435, 435e, 440e Carburetor Adjustment and Repair