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.
These show the principle for the design and function of the carburetor.
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).
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).
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).
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
- 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).
Dismantling the carburetor
- Dismantle the cylinder cover and the air ﬁlter.
- Disassemble the handle holder (see ﬁgure 29).
- Push the throttle actuator rod out of the handle part. Unhook it from the carburettor (see ﬁgure 30).
- 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).
Take care when lifting out the carburetor so that the fuel hose does not become loose.
- Loosen the screws (E) and unhook the rubber mountings (F) (see ﬁgure 32).
- Disassemble the pump cover (G) over the measuring chamber cover (R) and carefully remove the control diaphragm (H) with gasket (J).
- Unscrew the screw (K) and remove the needle valve (L) with the lever (M), shaft (N) and spring (P).
- Unscrew the screw (Q) above the pump unit and carefully remove the gasket (S) and diaphragm (T).
- Use a needle or similar device and carefully pull up the fuel screen (U).
- Unscrew the high (V) and low jet screws (W) (see ﬁgure 34).
- If necessary, dismount the throttle valve (X), choke valve (Z) and air shutter (Y) and remove the shafts with levers and springs (see
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:
- That gaskets, pump, and control diaphragms are undamaged.
- That there is no play on the throttle and choke valve shafts.
- That the needle valve (L) and its lever (M) are not worn (see ﬁgure 33).
- That the fuel screen (U) is whole and clean (see ﬁgure 33).
- That the tips of the high (V) and low jet screws
(W) are not damaged (see ﬁgure 34).
- That the intake manifold (R2) is undamaged (see ﬁgure 33).
- The carburetor has an extra air shutter connected in parallel with the ordinary throttle valve.
Maintain a high level of cleanliness when assembling the carburetor. The slightest contamination can result in running problems.
- 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.
- 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.
- Fit the fuel ﬁlter (U) by using the handle of a small screwdriver. (see ﬁgure 33)
- Fit pump cover (G), gasket (S) and measuring chamber cover (R) over the pump unit (see ﬁgure 33).
- 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).
- 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).
- Fit the control diaphragm (T) with gasket (S) and measuring chamber cover (R) over the metering unit (see ﬁgure 37).
- Press in the screen (U). Fit the measuring chamber cover (R) and tighten the screw (Q) (see ﬁgure 37).
- Put together the gasket (J) and control diaphragm (H) and press up (see ﬁgure 37).
- Assemble all the parts and tighten the four screws (see ﬁgure 37).
11.. Carry out a pressure test.
Pressure testing the carburetor
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:
Set the high and low jet screws two turns from the bottom.
Connect pressure tester to the carburettor’s fuel intake.
Lower the carburettor into a beaker of water (see ﬁgure 37).
Pump the pressure up to 50 kPa.
No leakage is permitted. If a leakage occurs refer to the table below.
Leakage in impulse tube Ventilation hole
on the metering unit.
Needle valve Pump diaphragm
Assemble on the saw
- Press the carburettor down towards the partition wall. Make sure that it gets into the correct position.
- Fit the ﬁlter holder by hooking the choke control into the choke lever (A).
- Hook on the rubber mountings. Insert and tighten the screws.
- Insert the return hose (B) into its position in the ﬁlter holder.
- Press on the fuel diaphragm (D). Fit the suction hose (C) and return hose (B).
- 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.
- Push down the handle holder into the ﬁlter holder (see ﬁgure 42).
- Assemble the air ﬁlter and cylinder cover.
- Mount the handle holder.
Carburettor adjustment Conditions during adjustment
- 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).
- The chain should not be tensioned more than that it remains ~ 0,2 inches to the bar.
(See ﬁgure 43)
Replacement of the H-needle or complete carburetor
- Carefully screw the new H-needle to the bottom and turn it anticlockwise ”A” turns.
435/e A = 2
440e A = 2
- Start the engine. If necessary, adjust the idling speed with the T-screw until the chain stops.
- 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.
- 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