Stihl 4-MIX Troubleshooting And Repair Instructions
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Stihl 4-MIX Troubleshooting And Repair Instructions

Stihl 4-MIX Troubleshooting And Repair Instructions

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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®
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 the technician in performing a step by step
analysis of the machine.
Repair Procedures: Quick Check
The fastest way to find any major fault is to quickly check for compression, ignition, spark,
and fuel delivery.
Use a spark tester to verify that spark is present.
If the engine has no spark, the spark plug, the ignition module or stop switch
system is at fault.
If the fuel system is completely restricted, the engine may not fire at all when trying
to start it. Squirt some choke spray in the carburetor and try to start the engine.
Does the engine have any
compression?
On
4-MIX®
engines, if compression feels low, or if the spark is okay and fuel is getting to
the engine, then do a leak down test.
This only takes a few minutes. If the leak down is below 10%, then the combustion
chamber is okay and the running problems are due to something else.
If the leak down is greater than 10%, the problem needs to be repaired, as well as
making sure that there are no other faults present.
If leak down is less than 10%
on a 4-MIX
faults elsewhere.
engines outline testing procedures as well as special tools that
Is fuel getting to the
combustion chamber?
®
engine, check for
Does the engine have
spark?
If leak down is greater than 10%, the
engine will need service, but check for
any other faults before doing any
repair.

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Summary of Contents for Stihl 4-MIX

  • Page 1 The STIHL troubleshooting video and corresponding iCademy module are ideal checklists to use when performing repairs and will assist the technician in performing a step by step analysis of the machine.

  • Page 2: Throttle Operation

    Click to download the STIHL 4-MIX® Engine Check Worksheet. The STIHL 4-MIX® Engine Check Worksheet is a simple guide to verify any faults found in a logical and efficient manner. Worksheets are available for both 2-cycle and 4-MIX® engines. An accurate repair cost estimate can then be prepared.

  • Page 3: Ignition Module

    Check for spark. The spark plug must be installed in the cylinder when performing an ignition module test with the STIHL ZAT 4. Holding the plug against the cylinder and pulling the starter rope is not a valid test of an ignition module.

  • Page 4: Air Filters

    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. The final verification of a faulty ignition module may have to be done by replacing it with a known good ignition module for comparison.

  • Page 5: Valve Clearance

    The specification for the ignition module to flywheel air gap is eight thousandths of an inch for all 4-MIX® engines. The STIHL setting gauge can be used to check and properly adjust the air gap. STIHL Part # 4118 890 6401. Backpack Blowers Shafted Products...
  • Page 6 A rushing air sound should be evident at one of these locations, verifying the location of the leakage from the engine. The leak down tester recommended by STIHL has a smaller air inlet orifice and is designed for testing any small engine.

  • Page 7: Impulse Line

    To perform a crankcase pressure and vacuum test the intake port and exhaust port must be sealed with the proper blocking tools. STIHL 4-MIX® engines need to also have the valve cover installed. Gauge readings.
  • Page 8 ZAMA ZPG-1. This will allow any internal faults in the carburetor to be identified quickly. Worn Mounting Surface Worn Throttle Shaft Fuel Leak Indicated by Dirt Build-up Three step evaluation for a 4-MIX® engine used on shafted products.
  • Page 9 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.
  • Page 10 Install the flywheel puller, part number 1116 893 0800, until it seats against the flywheel, then back it off one full turn. Hit it squarely with a ball peen hammer to release the flywheel from the crankshaft. Do not use an impact wrench on any STIHL product.
  • Page 11 Do not use an impact wrench on any STIHL product. Engine De-Carbonizing Procedure. If a 4-MIX® engine is showing more than 10% leakage past the exhaust valve, the most likely cause is carbon build-up on the valve face. STIHL Engine Decarbonizing liquid can be used to soften and flush out carbon deposits.
  • Page 12 If the engine is being assembled and the flywheel is not in place yet, just be sure the piston is at top dead center to time the cam correctly. To install the cam on the backpack blower engines, notice that when the piston is at top dead center, the cam lobe is pointing up when the alignment marks are matched up.

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