Install in the reverse sequence. Install new gaskets. This makes adjustment of the prescribed idle speed difficult, if not impossible. Moreover, the transition from idle speed to part or full throttle is not smooth. The engine housing can be checked thoroughly for leaks with the carburetor and crankcase tester and the vacuum pump, b Defective oil seals and gaskets or cracks in castings are the usual causes of leaks.
Such faults allow supplementary air to enter the engine and upset the fuel-air mixture. The sealing plate must completely fill the space between the two mounting screws. Oil seals tend to fail when subjected to a vacuum, i. A test can be carried out with the vacuum pump to detect this kind of fault. If this pressure remains constant for at least 20 seconds, the crankcase is airtight.
If the pressure drops, the leak must be found and the faulty part replaced. To find the leak, coat the suspect area with oil and pressurize the crankcase again. Bubbles will appear if a leak exists. If the vacuum reading remains constant, or rises to no more than 0. However, if the pressure continues to rise reduced vacuum in the crankcase , the oil seals must be replaced. It is not necessary to disassemble the complete engine if only the oil seals have to be replaced.
Take care not to damage the crankshaft stub. Important: Do not use a press to install the hard oil seal Install hard oil seals as described in b 6. Ignition side — Remove the flywheel, b 7.
Always check and, if necessary, repair the fuel system, carburetor, air filter and ignition system before looking for faults on the engine. If the engine pan is damaged, it must be replaced before installing the cylinder. Perform the following operations to replace the engine pan:. Make sure that ball bearings and oil seals are correctly seated.
If a new cylinder is installed, also install a new piston, b 6. If the piston pin is stuck, release it by tapping the end of the drift lightly with a hammer. Hold the piston steady during this process to ensure that no jolts are transmitted to the connecting rod. Inner pin must again point toward flat face. This means the crankshaft must always be replaced as a complete unit.
When fitting a replacement crankshaft, always install new ball bearings, oil seals and needle bearing. Exercise extreme caution when troubleshooting and carrying out maintenance or repair work on the ignition system.
The high voltages which occur can cause serious or even fatal accidents! The electronic breakerless ignition system basically consists of an ignition module 1 and flywheel 2. Since there is no mechanical wear in these systems, ignition timing cannot get out of adjustment as a result of wear. The ignition module accommodates all the components required to control ignition timing.
There are two electrical connections on the coil body:. Testing in the workshop is limited to a spark test. A new ignition module must be installed if no ignition spark is obtained after checking that wiring and stop switch are in good condition.. To test the ignition module, use either the ZAT 4 ignition system tester or the ZAT 3 ignition system tester Install all other parts in the reverse sequence.
Using the ZAT 4 ignition tester — Before starting the test, install a new spark plug in the cylinder and tighten it down firmly, b 3. The engine may start and accelerate during the test. If a spark is visible, the ignition system is in order. If no spark is visible in the window 2 , check the ignition system with the aid of the troubleshooting chart, b 7. While using the ZAT 3, hold it only by the handle 4 or position it in a safe place.
Keep fingers or other parts of your body at least 1 cm away from the spark window 3 , high voltage connection 2 , ground connection 5 and the ground terminal 1. High voltage — risk of electrocution. Using the ZAT 3 ignition tester — Before starting the test, install a new spark plug in the cylinder and tighten it down firmly, b 3. If no spark is visible in the window 3 , check the ignition system with the aid of the troubleshooting chart, b 7.
Replace flywheel if necessary. When installing, push grommet 1 sideways into the housing recess arrows. The wiring harness 2 must be on the right of the ignition lead 3. Check the spark plug: — Smeared with oil, black? Clean the plug, reset or replace. Check spark plug boot: — Firmly seated on plug leg spring? Check ignition lead: — Severe chafing? Look for fault in fuel system or carburetor, check engine for leaks, check position of flywheel on crankshaft.
If the action of the starter rope becomes very stiff and the rope rewinds very slowly or not completely, it can be assumed that the starter mechanism is in order but plugged with dirt.
At very low outside temperatures the lubricating oil on the rewind spring may thicken and cause the spring windings to stick together. This has a detrimental effect on the function of the starter mechanism.
In such a case it is sufficient to apply a few drops of a standard solvent-based degreasant containing no chlorinated or halogenated hydrocarbons to the rewind spring. Carefully pull out the starter rope several times and allow it to rewind until its normal smooth action is restored. Clean all components, b The hand guard is secured to the fan housing and engine housing with an IS-D5x24 screw and sleeve.
If clogged with dirt or pitch, the entire starter mechanism, including the rewind spring, must be removed and disassembled. Take particular care when removing the spring. Relieving tension of rewind spring The rewind spring will not be under tension if the starter rope is broken — Pull out the starter rope about 5 cm and hold the rope rotor steady.
When the starter rope is fully extended, it must still be possible to rotate the rope rotor at least another half turn before maximum spring tension is reached. If this is not the case, pull the rope out, hold the rope rotor steady and take off one turn of the rope.
Do not overtension the rewind spring as this will cause it to break. The rewind spring is correctly tensioned when the starter grip sits firmly in the rope guide bushing arrow without drooping to one side. If this is not the case, tension the spring by one additional turn. Wear on the guide bushing is accelerated by the starter rope being pulled sideways. The wall of the bushing eventually wears through and the bushing becomes loose. The installing tool flares the lower end of the rope bushing.
If the handle housing is being replaced because of damage, carry out the following additional operations:. Pull the impulse hose into position so that its flat rear side locates against the engine housing. Check that impulse hose and suction hose have no kinks. Make sure the short circuit and ground wires are positioned correctly.
Rubber anti-vibration buffers are installed between the engine housing, handle housing and front handle. Damaged rubber buffers annular buffers must always be replaced in sets. Check correct installed position of short circuit wire arrows. The torsion spring must be under the interlock lever and engage the notch. This prevents the oil pump from supplying sufficient oil to the bar and chain. In the event of problems with the oil supply system, first check the oil tank and the pickup body.
Clean the oil tank if necessary. Collect chain oil in a clean container. If necessary, dispose of it properly at an approved disposal site. A valve is installed in the tank wall to keep internal tank pressure equal to atmospheric pressure. Reassemble all other parts in the reverse sequence. Replacing the valve — Collect chain oil in a clean container. Machines up to Machines from : Carefully disconnect nipple 1 of cap retainer from the guide 2 in the engine housing.
Check the suction hose and pickup body are clean before disassembling the oil pump, b The elbow connector must snap audibly into position. Dirty air filters reduce engine power, increase fuel consumption and make starting more difficult. The air filter should be cleaned when there is a noticeable loss of engine power. Always install new O-rings. Knock out the filter or blow the two halves clear with compressed air from the inside outwards.
In the case of problems with the carburetor or fuel supply system, also check and clean, b The carburetor can be tested for leaks with the carburetor and crankcase tester If this pressure remains constant, the carburetor is airtight. However, if it drops, there are two possible causes:. The inlet needle is not sealing foreign matter in valve seat or sealing cone of inlet needle is damaged or inlet control lever sticking. Remove to clean, b Metering diaphragm damaged, replace if necessary, b The diaphragm material as well as the inlet and outlet valves are subjected to continuous alternating stresses and eventually show signs of fatigue, i.
There is a small spring under the inlet control lever which may pop out during disassembly. The upper face of the inlet control lever must be flush with the top of the carburetor body. The pump diaphragm, gasket and end cover are held in position by integrally cast pegs. If necessary, use a needle to take it out of the carburetor and clean or replace.
Standard setting without tachometer To readjust the carburetor, start with the standard setting. Then make the following adjustments: — Open high speed screw H one full turn.
If no tachometer is available, do not turn the high speed screw H beyond the standard setting to make the mixture leaner. Standard setting with tachometer — Check the air filter and clean or replace as necessary. Adjusting idle speed — Adjust idle speed with a tachometer. Adjust engine speed with idle speed screw LA to 3, rpm.
Turn low speed screw L clockwise or counterclockwise to obtain maximum engine speed. This manual is available in the following languages: English. Is your question not listed? Read Instruction Ma nual thoroughly before.
Ask a question. Leroy Bartmess, 1 comment 0. What fuel ratio does it need. Jerry Bush, Answer this question Send. About the Stihl MS Stihl MS specifications. Related product manuals. What is the weight of the Stihl MS ? The Stihl MS has a weight of g.
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