Harley Davidson Dyna evolution 1991-1998. Service manual - page 6
Fuel Level System
The fuel level system is shown in Figure 78. Proper carburetor operation
depends on a constant and correct carburetor fuel level. As fuel is
drawn from the float bowl during engine operation, the float level in
the bowl drops. As the float drops, the fuel valve moves away from its
seat and allows fuel to flow through the seat into the float bowl. Fuel
entering the float bowl will cause the float to rise and push against
the fuel valve. When the fuel level reaches a predetermined level, the
fuel valve is pushed against the seat to prevent the float bowl from
overfilling.
If the fuel valve doesn’t close, the engine will run too rich or flood
with fuel. Symptoms of this problem are rough running, excessive black
smoke and poor acceleration. This condition will sometimes clear up when
the engine is run at wide-open throttle, as the fuel is being used up
before the float bowl can overfill. As the engine speed is reduced,
however, the rich running condition repeats itself.
Figure 77 lists several things that can cause fuel overflow. In most
instances, it can be as simple a small piece of dirt trapped between the
fuel valve and seat or an incorrect float level. If you see fuel flowing
out of the overflow tube connected to the bottom of the float bowl, the
fuel valve inside the carburetor is being held open. First check the
position of the fuel valve lever. Turn the fuel valve lever OFF. Then
tap on the carburetor (not too hard) and turn the fuel valve lever back
ON. If the fuel flow stops running out of the overflow tube, you may
have dislodged whatever was holding the fuel valve off of its seat. If
fuel continues to flow from the overflow tube, remove and service the
carburetor. See Chapter Seven.
NOTE
On 1995 models, fuel will not flow from the vacuum operatedfuel valve
until the engine is running.
Starter or Choke System
A cold engine requires a very rich mixture to start and run properly. On
all models, a cable actuated enrichener valve is used for cold-starting.
The carburetor choke can also present a problem by causing difficult
cold starting. If the engine is difficult to start when cold, check the
choke cable adjustment described in Chapter Three. If the choke
cable adjustment is correct, refer to the possible
causes listed under Hard Starting in Figure 77.
Accelerator Pump System
Because the carburetor cannot supply enough fuel during sudden throttle
openings (quick acceleration), a lean air/fuel mixture will cause
hesitation and poor acceleration. To prevent this condition, factory
installed carburetors are equipped with a diaphragm type accelerator
pump system. See Figure 79. A spring-loaded neoprene diaphragm is
installed in a pump chamber at the bottom of the float
