Stihl 4 Mix Repair Manual

4-MIX® Troubleshooting and Repair  
 
Before any repair work is performed on a machine, a thorough evaluation should be made 
to determine what parts are actually in need of replacement or maintenance. The service 
manuals for STIHL 4-MIX® engines outline testing procedures as well as special tools that 
are needed to repair the equipment.  
 
The STIHL troubleshooting video and corresponding iCademy module are ideal checklists 
to use when performing repairs and will assist th e technician in performing...

 
Click to download the STIHL 4-MIX® Engine Check Worksheet
. 
 
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  The STIHL 4-MIX® Engine Check Worksheet is a simple guide to verify any faults found in a logical and efficient manner.  
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  Worksheets are available for both 2-cycle and  4-MIX® engines. 
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  An accurate repair cost estimate can then be prepared. 
 
Throttle Operation  
 
Verify that the throttle works smoothly, and that the  throttle interlock is working correctly. 
 
;
  The throttle cable should be adjusted so that the throttle is...

 
 
6
 
5
 
4
 
3
 
2
 
1
 
The throttle cable should always be checked for proper adjustment when a new machine is  
set up for delivery and anytime a machine is in for service. 
 
4282 Series – Throttle Cable Adjustment  
 
;
  If the throttle is not opening all the way on a backpack blower, performance and 
engine cooling will suffer. 
;
  To adjust the throttle cable on a  4-MIX® blower, turn the small screw that is located 
in the throttle trigger until the proper throttle opening is achieved....

;  If an incorrect spark plug is installed in a BR 600, the engine may quit after it warms up, or it may run poorly. It may also try to run-on when the ignition is switched off.  
;
  Set the gap on all STIHL spark plugs at twenty thousands of an inch. 
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  The final verification of a faulty ignition  module may have to be done by replacing it 
with a known good ignition module for comparison. 
 
FS 90, FS 100, FS 110, 
KM 110, FC 100, FC 110, 
HT 100, HT 101 , HL 100  FS 130, KM 130, 
HT 130, HT 131 
BR...

;  The shaft mounted 4-MIX® engines have a timing arrow on the flywheel that should 
point at the ignition module mounting screw as a reference point when the piston 
is at top dead center. 
;
  For the  4-MIX® blower engine the “S” marked corner on the flywheel should be just 
at the edge of the ignition armature leg when the piston is at top dead center. 
 
Shaft Mounted Engine 
 
 
Ignition Module Air Gap. 
 
;
  The specification for the ignition module to flywheel air gap is eight thousandths of an...

Check valve 
adjustments 
 
 
Leakage % is 
indicated on gauge 
that is connected 
to cylinder. 
 
Adjust regulator 
gauge to the set-
point. 
 
 
 
Engine - Leak Down Test  
 
Test the 4-MIX® engine  for leaks.  
 
Connect the gauge to the engine and read the amount of leakage.   
 
;
  There may be a little leakage past the end-gaps of the rings. If leakage is  less than 10% the sealing of the combustion chamber is acceptable.  
If leakage is over 10% you will need to identify the area of leakage and...

;  Install the rubber block off plate between the muffler gasket and the engine and install a flange adapter in place of the carburetor. Be sure to block the impulse 
hose.  
;
  When checking the crankcase for leaks, pressurize the crankcase to a reading of  positive 0.5 bar, or about 7 pounds per square inch. The pressure should not leak 
down to positive 0.3 bar, or about 4 pounds  per square inch, in 20 seconds. If it will 
not hold pressure or leaks down too fast, locate the leak with a soapy water...

;  If the starter is not assembled to the engine you can connect a carburetor testing gauge to the impulse hose when you perform a crankcase pressure and vacuum 
test.  
;
  The needle on the carburetor gauge should move as pressure and vacuum are  applied to the crankcase.   
 
If the impulse line becomes blocked, the running behavior of the engine will indicate 
carburetor problems, when in fact there may be none.  
 
 
 
 
Carburetors  
 
Inspect carburetor visually.  
 
;
  Before testing or...

;  Step 1: Hook the gauge to the inlet fitting on the carburetor, and 
pump it to no more than 10 PSI. The gauge reading should hold steady. If not, immerse  the carburetor in water and identify where it is leaking. If bubbles come out of the 
venturi, the inlet needle is leaking. If the bubbles come out around the fuel pump 
side or primer flange then the cause of the leak is most likely loose screws or 
damaged gaskets. The pressure gauge must hold steady at 10 PSI before 
performing step 2....

Accelerator 
Pump Bore 
Liquid 
Drawn In 
 
 
 
 
Fuel Tank  
 
Test fuel tank and tank vent.  
 
;
  It is a good practice to always pressure test an empty tank 
to be sure it has no leaks. Then perform a vacuum test to 
verify that the tank vent is allowing air into the tank.   
;  A poorly venting tank can cause running behavior such as 
engine stalling when hot, poor acceleration, or loss of power 
when hot.  
 
 
Special Service Procedures  
 
Special Tool Application: 10mm  Piston Stop, Flywheel...