The Husqvarna 445, 445E and 450E chainsaw service and repair troubleshooting guide will help with the repair and service of the carburetor. The carburetor may just need a clean, adjustment or replacing, this guide should help with this. A Service Manual detailing the carburetor removal, testing and refitting as well as more complete chainsaw repair information is available to download. Also a Parts List, Operator Manual, and carburetor manual are also available to view or download as a PDF which can be read on any device or printed.
Time taken for a medium skilled person to do this is about 30 minutes to 2 hours. The repair fully Covers the following Husqvarna chainsaw models:445, 445E and 450E.
Dismantling the carburetor
- Dismantle the cylinder cover and the air filter.
- Loosen the bolts (A).
- Loosen the filter holder from the rubber mountings (B).
(see figure 29)
- Loosen the suction hose (C) and return hose
(G) from the fuel pump.
- Dismantle the air shutter (D).
- Dismantle the throttle cable (E).
- Loosen the fuel hose (F).
(see figure 30)
- Dismantle the cover (A) on the metering unit and carefully remove the control diaphragm (B) with gasket.
- Dismantle the screw (F) and lift out the jet valve (E) with the lever (D), shaft (G) and spring (H).
- Dismantle the cover (K) on the pump unit and carefully remove the gasket (L) and diaphragms (M).
- Use a needle or the like and carefully remove the fuel screen (J).
- Dismantle the high (N) and low jet screws. (P)
- If necessary remove the throttle and choke valves, also dismantle the shafts with lever arms and springs.
(see figure 31)
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 (D) and its lever (E) are
not worn. (see figure 31)
- That the fuel screen (J) is whole and clean.
(see figure 31).
- That the tips of the high (N) and low jet screws
- are not damaged. (see figure 31)
- That the intake manifold is undamaged.
- The carburetor has an extra air shutter connected in parallel with the ordinary throttle valve. This is attached to the air ﬂange using two screws.
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 and low-speed needles and springs. Note! Do not fully tighten the screws. This will damage the seats and needle tips.
- Fit the fuel filter (J) by using the handle of a small screwdriver. (see figure 33)
- Fit the pump diaphragm (M), gasket (L) and
cover (K) on the pump unit. (see figure 33)
- Fit the needle valve (E) with the lever (D), pin and spring and tighten the screw (F). Fit welch plug
- (see figure 34).
- 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 35)
- Fit the control diaphragm (B) with gasket (C) and cover (A) on the metering unit. (see figure 36)
- Fit the throttle valve (U) on the shaft (R). Fit lever (S) on the shaft (R) parallel with the ordinary throttle valve. The valve housing (T) is secured in the air ﬂange using two screws. (see figure 32)
- 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 carburetor.
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 carburetor’s fuel intake.
Lower the carburetor into a beaker of water. (see
Pump the pressure up to 50 kPa (0.5 bar).
No leakage is permitted. If leakage occurs refer to the table below.
Leakage in impulse tube Ventilation hole
on the metering unit.
Needle valve Pump diaphragm
Replacing the bimetal 1
Release the locking sleeve (A) using a screwdriver.
(see figure 38)
Dismantle the bimetal (B). (see figure 38)
Fit the new bimetal. Ensure that it is seated correctly. (see figure 39)
Assembling the locking sleeve. (A) (see figure 38)
Assemble on the saw
- Assemble the fuel pump and suction hose on the carburetor.
- Assemble the fuel hose. (F)
- Position the carburetor.
- Fit the return hose (G) on the fuel pump.
- Fit the throttle cable. (E)
(see figure 40)
- Assemble the filter holder in the rubber mountings. (B)
- Snap the purge into the filter holder.
- Secure the screws. (A)
(see figure 41)
- Assemble the air filter and cylinder cover.
Carburetor adjustment Conditions during adjustment
- The air filter should be clean and the cylinder cover fitted when adjustments are made. Adjusting the carburetor 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 42)
Replacement of the H-needle or complete carburetor
- Carefully screw the new H-needle to the bottom and turn it anticlockwise ”A” turns.
445/e A = 2
450e 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.
445/e B = 12500 -13 000, speed limitation 450e 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.
445/e D = 2
450e D = 2
(see figure 43)
Carburetor service for Husqvarna 445 445e 450e chainsaws