Emissions
Fuel System
Section 3D - Emissions
Table of Contents
Exhaust Emission Standards...........................3D-2
What Are Emissions?...............................3D-2
Manufacturers Responsibility...................3D-3
Dealer Responsibility................................3D-3 3
Hydrocarbons – HC..................................3D-2
Carbon Monoxide – CO............................3D-2
Owner Responsibility................................3D-4
Exceptions................................................3D-4
D
Oxides of Nitrogen - NOx.........................3D-2 EPA Emission Regulations.......................3D-4
Controlling Emissions...............................3D-2 Manufacturer's Certificate Label......................3D-5
Stoichiometric (14.7:1) Air/Fuel Ratio.......3D-3 Family Number.........................................3D-5
Outboard Hydrocarbon Emissions Reduction Service Replacement Certification Label.........3D-5
.........................................................................3D-3 Removal...................................................3D-5
Emissions Information.....................................3D-3 Date Code Identification...........................3D-6
Installation................................................3D-6
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Emissions
Exhaust Emission Standards
Through the Environmental Protection Agency (EPA), the federal government has
established exhaust emissions standards for all new marine engines sold in the U.S.
What Are Emissions?
Emissions are what comes out of the exhaust system in the exhaust gas when the engine
is running. They are formed as a result of the process of combustion or incomplete
combustion. To understand exhaust gas emissions, remember that both air and fuel are
made of several elements. Air contains oxygen and nitrogen among other elements;
gasoline contains mainly hydrogen and carbon. These four elements combine chemically
during combustion. If combustion were complete, the mixture of air and gasoline would
result in these emissions: water, carbon dioxide and nitrogen, which are not harmful to the
environment. But combustion is not usually complete. Also, potentially harmful gases can
be formed during and after combustion.
All marine engines must reduce the emission of certain pollutants, or potentially harmful
gases, in the exhaust to conform with levels legislated by the EPA. Emissions standards
become more stringent each year. Standards are set primarily with regard to three
emissions: hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx).
Hydrocarbons – HC
Gasoline is a hydrocarbon fuel. The two elements of hydrogen and carbon are burned
during combustion in combination with oxygen. But they are not totally consumed. Some
pass through the combustion chamber and exit the exhaust system as unburned gases
known as hydrocarbons.
Carbon Monoxide – CO
Carbon is one of the elements that make up the fuel burned in the engine along with oxygen
during the combustion process. If the carbon in the gasoline could combine with enough
oxygen (one carbon atom with two oxygen atoms), it would come out of the engine in the
form of carbon dioxide (CO2). CO2 is a harmless gas. But carbon often combines with
insufficient oxygen (one carbon atom with one oxygen atom). This forms carbon monoxide,
CO. Carbon monoxide is the product of incomplete combustion and is a dangerous,
potentially lethal gas.
Oxides of Nitrogen - NOx
NOx is a slightly different by-product of combustion. Nitrogen is one of the elements that
makes up the air going into the engine. Under extremely high temperatures it combines
with oxygen to form oxides of nitrogen (NOx). This happens in the engines combustion
chambers when temperatures are too high. NOx itself is not harmful, but when exposed to
sunlight it combines with unburned hydrocarbons to create the visible air pollutant known
as smog. Smog is a serious problem in California as well as many other heavily populated
areas of the United States.
Controlling Emissions
There are two principle methods of reducing emissions from a two-stroke-cycle marine
engine. The first method is to control the air/fuel ratio that goes into the combustion
chamber. The second is to control the time when this air/fuel mixture enters the combustion
chamber. Timing is important, to prevent any unburned mixture from escaping out of the
exhaust port.
Page 3D-2 90-896580300 JULY 2004
Emissions
Stoichiometric (14.7:1) Air/Fuel Ratio
In the search to control pollutants and reduce exhaust emissions, engineers have
discovered that they can be reduced effectively if a gasoline engine operates at an air/fuel
ratio of 14.7:1. The technical term for this ideal ratio is stoichiometric. An air/fuel ratio of
14.7:1 provides the best control of all three elements in the exhaust under almost all
conditions. The HC and CO content of the exhaust gas is influenced significantly by the
air/fuel ratio. At an air/fuel ratio leaner than 14.7:1, HC and CO levels are low, but with a
ratio richer than 14.7:1 they rise rapidly. It would seem that controlling HC and CO by
themselves might not be such a difficult task; the air/fuel ratio only needs to be kept leaner
than 14.7:1. However, there is also NOx to consider.
As the air/fuel ratio becomes leaner, combustion temperatures increase. Higher
combustion temperatures raise the NOx content of the exhaust. But, enrichening the air/
fuel ratio to decrease combustion temperatures and reduce NOx also increases HC and
CO, as well as lowering fuel economy. So the solution to controlling NOx - as well as HC
and CO - is to keep the air/fuel ratio as close to 14.7:1 as possible.
Outboard Hydrocarbon Emissions Reduction
120
100
80
60
40
20
0 ob01313
96 97 98 99 2000 01 02 03 04 05 06 07 08
8 1/3% Change Per Year Over 9 Model Years
Emissions Information
Manufacturers Responsibility
Beginning with 1998 model year engines, manufacturers of all marine propulsion engines
must determine the exhaust emission levels for each engine horsepower family and certify
these engines with the United States Environmental Protection Agency (EPA). A
certification decal/emissions control information label, showing emission levels and engine
specifications directly related to emissions, must be placed on each engine at the time of
manufacture.
Dealer Responsibility
When performing service on all 1998 and later outboards that carry a certification, attention
must be given to any adjustments that are made that affect emission levels.
Adjustments must be kept within published factory specifications.
90-896580300 JULY 2004 Page 3D-3
Emissions
Replacement or repair of any emission related component must be executed in a manner
that maintains emission levels within the prescribed certification standards.
Dealers are not to modify the engine in any manner that would alter the horsepower or
allow emission levels to exceed their predetermined factory specifications.
Exceptions include manufacturers prescribed changes, such as that for altitude
adjustments.
Owner Responsibility
The owner/operator is required to have engine maintenance performed to maintain
emission levels within prescribed certification standards.
The owner/operator is not to modify the engine in any manner that would alter the
horsepower or allow emissions levels to exceed their predetermined factory specifications.
Exceptions
• Carburetor jets may be changed for high altitude use in accordance with factory
recommendations.
• Single engine exceptions may be allowed with permission from the EPA for racing and
testing.
EPA Emission Regulations
All new 1998 and later outboards manufactured by Mercury Marine are certified to the
United States Environmental Protection Agency as conforming to the requirements of the
regulations for the control of air pollution from new outboard motors. This certification is
contingent on certain adjustments being set to factory standards. For this reason, the
factory procedure for servicing the product must be strictly followed and, whenever
practicable, returned to the original intent of the design.
The responsibilities listed above are general and in no way a complete listing of the rules
and regulations pertaining to the EPA laws on exhaust emissions for marine products. For
more detailed information on this subject, you may contact the following locations:
VIA U.S. POSTAL SERVICE:
Office of Mobile Sources Engine Programs and Compliance Division Engine Compliance
Programs Group (6403J)
401 M St. NW
Washington, DC 20460,
VIA EXPRESS or COURIER MAIL:
Office of Mobile Sources Engine Programs and Compliance Division Engine Compliance
Programs Group (6403J)
501 3rd St. NW
Washington, DC 20001,
EPA INTERNET WEB SITE: http:/www.epa.gov/omswww
Page 3D-4 90-896580300 JULY 2004
Emissions
Manufacturer's Certificate Label
The certification label must be placed on each engine at the time of manufacture and must
be replaced in the same location if damaged or removed. Shown below is a typical
certification label and is not representative of any one model. Label shown below is not to
scale.
a
f
b g
c h
d i
e
ob00366
a- Idle speed f - Family Number
b- Engine horsepower g - Maximum emissions output for the
c- Piston displacement engine family
d- Date of Manufacture h - Timing specifications
e- Valve Clearance (if applicable) i - Recommended spark plug and gap
Family Number
The following is a illustration of a typical family number and is not a representation of any
one model.
1 3 M9X M 03.4 2 G 0 7
2 3 4 5 6 ob01314
1- Model year (3 = 2003) 5 - Technology type ( 1 = OB old tech,
2- Manufacturer (Mercury Marine) 2 = OB new tech, 3 = SportJet, 4 =
3- Regulations (M = Marine) OptiJet)
4- Engine displacement (Decimal 6 - Engine class (C = two stroke, G =
point = Liters [03.4 = 3.4L]) (No four stroke)
decimal point = C.I. [0113 = 113 7 - Product type (0 = all except, J =
Cubic Inches]) SportJet, E = EFI SportJet and 4
strokes, 3 = OptiMax, H = high
performance)
Service Replacement Certification Label
IMPORTANT: By federal law, it is required that all 1998 and newer Mercury Marine
outboards have a visible and legible emission certification label. If this label is missing or
damaged, contact Mercury Marine Service for a replacement.
Removal
Remove all remaining pieces of the damaged or illegible label. Do not install new label over
the old label. Use a suitable solvent to remove any traces of the old label adhesive from
the display location.
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Emissions
Date Code Identification
Cut and remove a "V" notch through the month of engine manufacture before installing the
new label. The month of manufacture can be found on the old label. If the label is missing
or the date code illegible, contact Mercury Marine Technical Service for assistance.
Emission Control
Information
THIS ENGINE CONFORMS TO 2005 CALIFORNIA AND U.S EPA
EMISSION REGULATIONS FOR SPARK IGNITION MARINE ENGINES
REFER TO OWNERS'S MANUAL FOR MAINTENANCE
SPECIFICATIONS AND ADJUSTMENTS
IDLE SPEED (in gear) 550 FAMILY: 5M902.62GO
250 HP 2598 cc FEL: 16.1100 g/kWh
TIMING (IN DEGREES): NOT ADJUSTABLE
JUN SPARK PLUG: NGK ILFR6G
2004 GAP: MM (.32")
COLD VALVE INTAKE: 0.15 - 0.23 MM
CLEARANCE (mm) EXHAUST: 0.35 - 0.43 MM
JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC b
5648
a
a - "V" notch b - Month of manufacture
Installation
Install the label on a clean surface in the original factory location.
Model Service Part Number Location on Engine
2005 Mercury/Mariner 200/225/250/275 EFI (4-Stroke) Verado 37-895282A05 Electrical box cover
Page 3D-6 90-896580300 JULY 2004
