Table of Contents
Advertisement
FUEL DELIVERY
as the engine, warranty coverage may become void if other
brands are substituted.
Grease should be cleaned from parts and fresh grease applied
before reassembly of components. Deteriorating grease loses
lubricity and may contain abrasive foreign matter.
Whenever removing or reinstalling batteries, care should be
taken to avoid the possibility of explosion resulting in serious
burns. Always disconnect the negative (black) cable first and
reconnect it last. Battery electrolyte contains sulfuric acid and
is poisonous! Serious burns can result from contact with the
skin, eyes or clothing. ANTIDOTE: External - Flush with
water. Internal - Drink large quantities or water or milk. Follow
with milk of magnesia, beaten egg, or vegetable oil. Call
physician immediately. Eyes - Flush with water for 15 minutes
and get prompt medical attention.
FUEL DELIVERY SYSTEM
(CARBURETED)
Carbureted System Overview
The carbureted fuel system contains many components which
directly affect fuel mixture and performance. When performing
diagnosis or carburetor maintenance, the entire fuel delivery
system should be inspected.
Fuel filters should be replaced at least once per season. More
often if contamination is suspected.
Fuel lines should be replaced every other season. More often if
they become brittle or swollen. Fittings should be inspected for
cracks or leaks. Do not use pliers or other tools that may damage
fuel lines when installing or removing fuel lines.
Test run and check the fuel system for leaks any time parts are
replaced. Verify that all lines are routed correctly and away from
any moving parts.
NOTE: Some models use fuel filters that are located
inside the fuel tank. To inspect/replace filter, remove
fuel cap and use a long clean wire, bend one end
into a hook shape. Pull the fuel line that is in the
tank up through the filler hole. Inspect filter on end
of fuel pick up line. Replace if worn or clogged.
Red fuel line is the exterior line for outside the tank. The violet
line is the interior line for inside the fuel tank. They cannot be
interchanged! The violet line used inside the tank will fade and
turn clear after a relatively short time. This does not affect the
function or durability of the line.
4.4
When replacing fuel line, be sure to use the correct color line for
inside or outside the fuel tank. Also, be very careful not to bend
fuel line to a point of kinking it. If it becomes kinked, it must be
replaced. Always inspect fuel lines when replacing, or if carbs,
carburetor racks, or fuel pumps are removed from chassis.
FUEL PUMP (CARBURETED UNITS)
Fuel Pump Overview
The differences are in the size and
location of the pumps. Pumps may
be mounted to the engine, air/oil box
or to the chassis.
In the two cycle engine, the pressure
in the crankcase changes with the up
and down stroke of the piston. The
amplitudes
of
pressure
according to the RPM and degree of
throttle opening. Whether idling or at
full throttle, the pressure built up in
the crankcase has enough amplitude
to operate the pump.
When the piston is on the upstroke,
crankcase pressure in that cylinder
becomes
less
positive.
diaphragm in the fuel pump moves
toward the engine, causing a
negative pressure or suction in the
pump chamber. This causes the inlet
valve from the fuel supply to open
and permits fuel to enter the chamber. This same suction causes
the outlet valve (to the carburetor) to close so that fuel cannot
return to the carburetor. (340/550 style shown)
When the piston begins its downward stroke, the pressure from
the crankcase becomes positive, causing the fuel pump
diaphragm to move in the opposite direction and reversing the
pressure in the fuel pump chamber. This causes the inlet valve
in the pump to close and the outlet valve to open, filling the float
bowl in the carburetor. When the float level in the carburetor
reaches its standard level, the needle valve will close,
preventing more fuel from entering the carburetor, even though
the fuel pump continues to try to provide the carburetor with
fuel.
vary
The
Advertisement
Chapters
Table of Contents
Troubleshooting
