Stihl 4-MIX User 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 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?
Is fuel getting to the
combustion chamber?
Does the engine have
spark?
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
®
engine, check for
faults elsewhere.
If leak down is greater than 10%, the
engine will need service, but check for
any other faults before doing any
repair.

Stihl 4-MIX Specifications

General

Valve Technology	Overhead valve (OHV)
Power Output	1.4 kW (1.9 hp)
Idle Speed	2, 800 rpm
Ignition System	Electronic ignition (CDI)
Oil Tank Volume	N/A (mixed fuel system)

Summary

4-MIX® Troubleshooting and Repair

Repair Procedures: Quick Check

Outlines a quick check for compression, ignition, spark, and fuel delivery.

Throttle Operation

4180 Series – Throttle Adjustment Procedure

Details how to adjust throttle cable on shaft-mounted products using adjuster cam.

4282 Series – Throttle Cable Adjustment

Ignition Module

Describes checking ignition module for faults and spark plug condition.

Air Filters

Flywheel

Discusses sheared flywheel key as a fault and verification of timing.

Ignition Module Air Gap

Valve Clearance

Explains valve clearance specification and checking procedure for 4-MIX® engines.

Engine - Leak Down Test

Crankcase - Vacuum & Pressure Test

Details testing the crankcase for leaks using pressure and vacuum.

Gauge readings

Impulse Line

Describes checking the impulse line for blockages using a pressure tester.

Carburetors

Three step evaluation for a 4-MIX® engine used on shafted products.

Outlines a three-step evaluation for carburetors on shafted products.

Step 1: Carburetor Inlet Pressure Test

Tests carburetor inlet pressure and checks for leaks with a gauge.

Step 2: Carburetor Metering Chamber Vacuum Test

Tests carburetor metering chamber vacuum by pumping the primer bulb.

Step 3: Purge Primer Check Valve Test

Verifies the outlet check valve in the purge primer flange is working correctly.

Accelerator Pump O-Ring Quick Test

Quickly checks the accelerator pump o-ring for leaks using soapy water.

Fuel Tank

Special Service Procedures

Details special tool application for 10mm piston stop and flywheel removal.

Remove Fan Wheel

Engine De-Carbonizing Procedure

Explains using decarbonizing liquid to remove carbon build-up on valve faces.

Cam Timing

Cam Timing for Backpack Blowers

Details aligning cam gear with notches and flywheel with ignition module for backpack blowers.