Outboard Hydrocarbon Emissions Reductions - Mercury 40 Service Manual

As the air/fuel ratio becomes leaner, combustion
temperatures increase. Higher combustion tempera-
tures raise the NOx content of the exhaust. But, enri-
chening the air/fuel ratio to decrease combustion
temperatures to 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.
8 1/3% # PER YEAR OVER 9 MODEL YEARS
120
100
80
60
40
20
0
96 97
FUEL SYSTEM - 3D-2
OUTBOARD HYDROCARBON
EMISSIONS REDUCTIONS
98 99 2000 01 02 03 04 05 06 07 08
90-852572R1 JANUARY 1998