Stihl 4-MIX Troubleshooting And Repair Instructions

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?

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.

®

engine, check for

Is fuel getting to the
combustion chamber?

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.

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.

;

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 opening all the way to

;

the stop on the carburetor without causing excessive tension on the cable.
Example A.

Be sure that the throttle returns to idle easily and smoothly.

;

On a shaft mounted 4-MIX® product, inspect the cable for fraying where it slides

;

over the plastic cam on the carburetor flange. Example B.

A

B

4180 Series – Throttle Adjustment Procedure

To adjust the throttle correctly on a shaft mounted product, set the screw on the

;

adjuster cam that is located on the carburetor flange so the same amount of
threads show on either side of the cam.

Next, using a small screwdriver, push down on the tab located in the top of the

;

throttle assembly and slide the tab towards the engine.

Now squeeze the throttle to the wide open position. The tab will slide forward and

;

automatically adjust the throttle cable. Release the throttle trigger and verify that
the throttle lever comes back fully to idle.

1

2

3

4

The throttle cable should always be checked for proper adjustment when a ne w machine is
set up for delivery and anytime a machine is in for service.

5

6

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.

Ignition Module

Check for spark with a spark tester that loads the ignition module.

Modules can have intermittent faults: Heat related failures where the spark returns

;

after the module cools down, or even show spark but not start the engine.

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.

Inspect the spark plug and verify heat range.

Verify that the correct spark plug is installed. The spark plug for an FS 100 is hotter

;

than the spark plug for a BR 600.

; 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.

;

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

STIHL 0000 400 7009
Bosch USR7AC

FS 130, KM 130,
HT 130, HT 131
BR 500, BR 550, BR 600

STIHL 0000 400 7011
NGK CMR6H

NGK CMR5H

Refer to the STIHL repair specification charts for other models.

Air Filters

Air filters should be inspected and cleaned regularly. Filters should be replaced at lea st
once a year, or more often if needed.

The air filter element used on the 4-MIX® shaft mounted engines should never be

;

cleaned in solvent. Brush off any loose debris and clean it with compressed air.

STIHL backpack blower engines use a pleated paper air filter. The only way to

;

service it is to brush off any debris or gently blow it off. Do not use high pressure
air or the pleats may tear.

Always inspect the clean side of the filter housing for any evidence of dirt or grit. If

;

dirt is present, the filter needs to be serviced more often.

Flywheel

Fault – A sheared flywheel key.

Occurs when: The nut is not properly tightened, or if an impact wrench is used to

;

loosen or tighten the fan wheel, flywheel, clutch, or starter cup nut.

A sheared key may not cause the ignition module to lose spark, so the spark tester

;

will not show a fault.

Verify flywheel timing.

Never use an
impact wrench
on any STIHL
product!