Chapter 4: The Fuel System and Governor
32
Evaporative (EVAP) emissions system
Gasoline is made from the graduated distillation of
crude oil. It consists of a multitude of individual hydro-
carbons and has a boiling range of 86 - 410
o
F (30-
210
o
C)
1
. The large quantity of hydrocarbons and the
low boiling range makes gasoline an ideal fuel for spark
ignited, internal combustion engines. However, the
hydrocarbons are not good for the environment. To
reduce or eliminate the release of fuel vapors into the
atmosphere, an evaporative (EVAP) emissions system
is used. Starting with the 2008 season, an EVAP sys-
tem has been offered in areas that require it. MTD has
two systems that can be used. The first one is a char-
coal canister system and the second (available starting
in the 2009 model year) is redesigned EVAP fuel tank.
The charcoal canister system can be identified by the
charcoal canister. See Figure 4.8.
The charcoal canister system consists of:
• A charcoal canister
• The fuel tank and cap
• A roll over valve vent
• A carburetor insulator.
• Vacuum lines
This system operates as follows:
1. The gasoline evaporate and lets off vapors.
2. The vapors exit the fuel tank through the roll
over valve vent.
NOTE: The fuel cap used with the charcoal can-
ister system is not vented. If a vented cap is
used, the EVAP system will not work.
See Figure 4.9.
3. The vapors are routed through the charcoal can-
ister. See Figure 4.10.
Figure 4.8
Charcoal canister
Roll over valve
Figure 4.9
Vented
Unvented
Figure 4.10
Charcoal canister
Vapor
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