Chapter 4: The Fuel System and Governor
29
The function of the fuel system is to store, mix the fuel
with air and deliver it to the combustion chamber. The
fuel system consists of the following components:
• Fuel tank
• Fuel lines
• Fuel filter
• Carburetor
NOTE: When working on the fuel systems, look
at the whole system. A problem will rarely be iso-
lated to one component.
Inspecting the fuel:
NOTE: Fuel is the maintenance item most often
overlooked by consumers. A lot of fuel systems
problems are caused by bad gas or too much
alcohol in it. When inspecting the fuel:
• Look for water.
• Look for dirt.
• Look for discoloration.
• Sniff carefully to see if it smells like varnish or
kerosene.
• Save the fuel to show to customer.
• Look for oil in the fuel.
• Test the fuel for alcohol content if there is a rea-
son to suspect it.
NOTE: Save a sample of the fuel collected to
show the customer.
NOTE: Customers pouring engine oil into the
fuel tank seems to be a growing problem.
Test fuel for alcohol:
Fuels currently on the market contain a wide array of
additives. Some of these additives oxygenate the fuel.
Oxygenated fuel reduces emissions, and is required in
some parts of the United States. Fuel make-up varies
seasonally and geographically. Ethanol is the primary
additive used to oxygenate fuel.
Ethanol in fuel creates a lot of problems for gasoline
engines. The biggest problem is that alcohol attracts
and holds water. This corrodes the metal components
of the fuel system, especially the carburetor. Alcohol
also does not produce as much heat as gasoline when
burnt. This results in less power for the engine.
A 10% ethanol (E10) mix is acceptable for MTD
engines. Anything higher than that will result in perfor-
mance issues.
NOTE: E20 and E85 fuels are not to be used in
any MTD engines.
There are several alcohol test kit available commer-
cially. See Figure 4.1.
Figure 4.1
CHAPTER 4: THE FUEL SYSTEM AND GOVERNOR
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