182
Two-Stroke Engines
Copyright Goodheart-Willcox Co., Inc.
Introduction
All two-stroke engines sold in the United States
since 2011 are tested and adjusted at the factory.
They are run to operating temperature, and the
carburetor is adjusted to emission standards.
The results of the tests are recorded electroni-
cally with the EPA, establishing documentation
that each piece of equipment has been emis-
sions certified.
During the test and adjustment procedure,
the PTO component of the equipment and its
operational load are attached. For example, a
string trimmer engine has the trimmer PTO
attached. The chain saw has the appropriate bar
and chain attached. The blower has the correct
blower tube(s) and the correct restrictor tube
attached.
When a piece of two-stroke equipment leaves
the factory, the engine is running properly, the
carburetor is precisely adjusted, and the PTO
component is working correctly. When two-
stroke equipment runs poorly or refuses to run
at all, the fault could be in the PTO component,
the engine, or both.
Troubleshooting involves identifying prob-
lems with a two-stroke engine and equipment.
The goal of the technician is to troubleshoot the
engine or equipment quickly and to get it back
into service as soon as possible. This means
accurately identifying problems so that extra
time is not spent making unnecessary repairs.
Evaluation, on the other hand, is generally
performed if the problem cannot be identified
during the troubleshooting process. Evaluation
involves systematically identifying engine sys-
tem or component conditions that are differ-
ent from those present when the unit left the
factory. Being thorough in identifying differ-
ences will help you pinpoint the cause(s) for a
non-running or poorly running engine.
NOTE
Problems with the equipment can cause the
engine to run poorly or not at all. Equipment
evaluation is part of the troubleshooting and
evaluation process. However, this chapter will
focus on troubleshooting and evaluating two-
stroke engines.
Recording Equipment and
Engine Information
During troubleshooting and evaluation pro-
cesses, equipment and engine identification
information should be written down, including
the following:
• Equipment numbers:
• Equipment model number.
• Equipment serial number.
• Engine numbers:
• Engine model number.
• Engine serial number.
• Any numbers on attachments.
Two-stroke equipment manufacturers con-
tinually update and upgrade their compo-
nents. Therefore, engine and equipment serial
numbers must be used to identify the correct
replacement parts. These numbers can also be
used to identify equipment that was attached to
the engine but was not designed for the engine.
The engine and equipment numbers are typ-
ically found in locations that are least affected
by weather or the normal operation of the
equipment. If a serial number is not found on
an engine’s data tag, it should be permanently
inscribed on the engine in a different location.
Refer to the repair manual for the location of
the engine’s model and serial numbers. In some
cases, the engine numbers are used to identify
both the engine and the equipment it powers.
See Figure 9-1.
In addition to recording equipment and engine
numbers, you should document conditions found
Goodheart-Willcox Publisher
Figure 9-1. On two-stroke equipment, the equip-
ment and engine are typically integrated as a unit.
The engine model and serial tag identifies the
equipment, not just the engine. The serial number
will help identify part numbers that have changed
on newer units.
Model Serial number