Motorcycle Troubleshooting

The ability to quickly and correctly troubleshoot motorcycle or ATV
problems is the first sign of a competent technician. Proper diagnosis
of a malfunction makes motorcycle or ATV disassemble, repair, and
reassembly relatively simple. If a malfunction has been improperly
diagnosed, the repair process can become long and tedious, or even
impossible. In order to be a successful technician, you must possess
proficient troubleshooting skills. First and foremost, troubleshooting
begins with a thorough knowledge of the
 Parts of a motorcycle
 Job each part performs
 Effect each part has on overall motorcycle operation
 Types of failure symptoms that a bad part will cause
Once you’ve gained this knowledge, troubleshooting becomes a
systematic and controlled approach to solving a problem.
When troubleshooting, you’ll need to
 Gather all available information about the machine’s
 Analyze the symptoms related to the problem
 Pinpoint the most likely cause of the problem
The repair process doesn’t begin until after you’ve gotten a clear
picture of what’s causing the problem. To achieve this picture, you’ll
have to
 Mentally divide the motorcycle into sections (carburetion,
engine, electrical, and chassis)
 Picture each component of every section
 Picture each component and its relationship to the other
components and decide if each part is functioning properly
For example, suppose a spark plug isn’t firing correctly. You must
envision the operation of the spark plug in relation to the other
motorcycle systems. After doing this, you’ll have a variety of possible
problems identified, besides the obvious conclusion that the spark
plug is bad. The problem could be due to a dirty air filter that’s
creating an excessively rich fuel mixture. The source of the problem
could also be the ignition circuit or the carburetor system.

It’s imperative that you understand what you’re trying to repair
before disassembling a machine. Once you begin the disassembly
process, the troubleshooting process is over. In our example, cleaning
and replacing parts in the carburetor won’t solve the problem if the
cause is a faulty ignition. Therefore, ensure that you’ve truly isolated
the problem before beginning any repair.
This section of the study unit concentrates on techniques that expedite
the process of troubleshooting motorcycle and ATV problems.
Developing a systematic approach to problem solving now will help
you to perfect your skills as you gain experience.
Types of Problems
A symptom is an indication of an abnormal condition that you can
recognize and identify. An example of a symptom would be a
motorcycle that’s making a ticking sound when it’s idling. The
symptom helps you determine the cause of the problem. The
following paragraphs cover three types of failures that you may
Constant Failures
A constant failure occurs when a symptom is always present. For
instance, a motorcycle is functioning properly and without warning,
the engine fails and the rear wheel locks up. The locked rear wheel is
considered a constant failure.
Intermittent Failures
An intermittent failure isn’t always present. This type of failure
increases the difficulty of the troubleshooting process. For example,
a particular motorcycle functions properly with the exception of
occasionally blowing a fuse when the vehicle hits a pothole. The rider
replaces the fuse and rides trouble-free until the problem recurs when
another large bump is encountered. Chances are, this intermittent
problem is caused by multiple factors. In this instance especially, a
systematic approach to troubleshooting the problem is required. With
any problem (performance, electrical, mechanical, or fuel), a systematic
approach allows the problem to be diagnosed in a reasonable amount
of time with a high degree of accuracy.

Improper-service Failures
An improper-service failure, as the name implies, is caused by a
technician who made a mistake during the servicing of the
equipment. Suppose a customer brings an off-road vehicle to your
service department for a new set of tires and the technician servicing
the vehicle fails to properly torque one of the wheel-retaining nuts
and forgets to install a cotter pin on the rear-axle nut. Later this
improper service causes the wheel to wobble and fall off while the
customer is riding the machine. Obviously, most failures caused by
improper service aren’t this dramatic. It’s important not to overlook
problems resulting from bad service when you’re troubleshooting a
Beginning the Troubleshooting Process
The proper method of diagnostic troubleshooting consists of four
steps that must be followed in the proper sequence. Follow these
steps for a foolproof approach to the troubleshooting and repair
1. Verify the problem.
2. Isolate the problem.
3. Repair the problem.
4. Verify the repair.
When troubleshooting, you must observe the failure and verify that
all of the information you’ve received is accurate and guides you to
the trouble area. After you’ve completed the verification stage, you’re
ready to begin the isolation phase.
Isolating a problem begins with the easiest and most obvious solution
to the problem. As the simplest solutions fail to correct the problem,
progression to more involved and difficult checks needs to be
performed in a step-by-step manner. The most common diagnostic
mistake is to overlook the obvious or easiest possible cause of a
failure. For example, a motorcycle was functioning properly, then
stalled and wouldn’t restart. The owner took the motorcycle to a
service station. The technician removed and checked the spark
plugs, checked the air filter, replaced the battery, and performed
compression and leakdown tests. When all was said and done, the
problem was an empty fuel tank. Believe it or not, this situation isn’t
uncommon and results from poor troubleshooting skills (not starting
with the simplest solutions first).
The symptoms of a problem guide you to the specific system you
should troubleshoot, provided you have an understanding of how
each system works and what it’s responsible for. For example,

 If the battery won’t turn the engine over, you can assume that
the machine has a worn-out battery or a charging system that’s
failing to provide a proper charge to the battery.
 If gasoline is leaking from the carburetor overflow tube, you can
assume that there’s an internal carburetor problem that’s
causing excessive amounts of gasoline to enter the system.
As the severity of problems increases, the knowledge required to
repair the problem increases. An example of this is poor engine
performance. A performance problem could be caused by an ignitionsystem
failure, a mechanical engine problem, or even a fuel-related
problem. It’s imperative to use all available resources and any
information you can gather from your customer to assist you in
identifying which system is responsible for the problem.
After you’ve isolated the problem, you must repair the problem. In
order to repair the problem, you must refer to the specific service
manual for the particular motorcycle or ATV you’re servicing. When
you complete the repair, you must verify the repair. If you can’t verify
that the repair was successful (the problem still occurs), you must
repeat the troubleshooting process, beginning with the verification
Troubleshooting Guides
The appropriate manufacturer’s service manual contains checklists or
tables of possible operating troubles and their probable causes. These
tables aid in troubleshooting and problem solving. All possibilities
should be carefully checked because multiple factors may be causing
the overall problem. Throughout this study unit, examples of typical
problems and possible solutions are provided. These examples have
been derived from current service manuals and technical guides.
However, you should note that the specific troubleshooting sections
of this study unit and in manufacturer’s service manuals are intended
only as a guide to diagnosing problems. Always read the detailed
information in the specific chapters of the appropriate service manual
before performing service work on any system or major component.
Remember to adhere to all cautions and warnings.
As you learn more about various motorcycle and ATV systems, you
may develop a tendency to troubleshoot problems based on your
personal experience. This approach is a gamble that can occasionally
save you time; but if you guess wrong, it costs you time and money.
Don’t be afraid to apply your experience to a good troubleshooting
routine, but don’t underestimate repairs because the failure looks

Locating and fixing a problem is very rewarding, provided you use
good troubleshooting techniques. Furthermore, the more difficult
the problem, the greater the reward when you’ve solved it. To be
successful, the most important barrier to overcome is the lack of
self-confidence required to perform the job. Here are some things to
keep in mind when you’re troubleshooting a problem.
 Always think the problem through.
 Never overlook the obvious.
 Never assume anything.
 Never take shortcuts.
 Never make more than one change or adjustment at a time.
 Always use the appropriate service manual(s) for all removals,
replacements, and adjustments.
 Remember to always verify the problem, isolate the problem,
repair the problem, and most importantly, verify the repair.
Road Test 1
At the end of each section of Motorcycle Troubleshooting, you’ll be asked to check your
understanding of what you’ve just read by completing a “Road Test.” Writing the answers
to these questions will help you review what you’ve learned so far. Please complete Road
Test 1 now.
1. Another word used to define a description of a problem is _______.
2. Where would you find a checklist or table of possible operating troubles and their
probable causes?
3. What are the four procedures that must be followed when developing the proper method
of diagnostic troubleshooting?
4. What are the three basic categories of troubleshooting problems on motorcycles and
5. What one barrier must be overcome before you can troubleshoot any type of problem?



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