78/83/90 Series Horizontal Shaft Engines
42
Evaporative (EVAP) emissions system
Gasoline is made from the graduated distillation of crude oil. It consists of a multitude of individual hydrocarbons
and has a boiling range of 86 - 410
°F (30-210°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.
Effective January 1, 2011; the EPA has mandated that all summer engines with 225cc’s of displacement or more
must be equipped with an evaporative emissions system.
The EVAP system used by MTD consists of:
• A charcoal canister
• The fuel tank and cap
• A roll over valve vent
• The control panel.
• Vacuum lines
Reference
1. Dr. Ullmann, J, Fuels, Automotive Handbook, seventh edition. Bosch, Robert distributed by SAE Society of
Automotive Engineers, 2007. 320.
Figure 4.8
Charcoal canister
Roll over valve
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