Yamaha YZ250F(D) Page 23 Owner'S Service Manual Download

Page: 23 / 198

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STARTING AND BREAK-IN

FUEL

Always use the recommended fuel as
stated below. Also, be sure to use
new gasoline the day of a race.

Use only unleaded gasoline. The
use of leaded gasoline will cause
severe damage to the engine inter-
nal parts such as valves, piston
rings, and exhaust system, etc.

If knocking or pinging occurs, use a
different brand of gasoline or higher
octane grade.

• For refueling, be sure to stop the

engine and use enough care not
to spill any fuel. Also be sure to
avoid refueling close to a fire.

• Refuel after the engine, exhaust

pipe, etc. have cooled off.

HANDLING NOTE

Never start or run the engine in a
closed area. The exhaust fumes
are poisonous; they can cause
loss of consciousness and death
in a very short time. Always oper-
ate the machine in a well-ventilated
area.

• The carburetor on this machine

has a built-in accelerator pump.
Therefore, when starting the en-
gine, do not operate the throttle
or the spark plug will foul.

• Unlike a two-stroke engine, this

engine cannot be kick started
when the throttle is open be-
cause the kickstarter may kick
back. Also, if the throttle is open
the air/fuel mixture may be too
lean for the engine to start.

• Before starting the machine, per-

form the checks in the pre-opera-
tion check list.

AIR FILTER MAINTENANCE

According to "CLEANING THE AIR
FILTER ELEMENT" section in the
CHAPTER 3, apply the foam-air-filter
oil or its equivalent to the element.
(Excess oil in the element may ad-
versely affect engine starting.)

STARTING A COLD ENGINE

1. Inspect the coolant level.
2. Turn the fuel cock to "ON".
3. Shift the transmission into neutral.
4. Fully open the cold starter knob

"1".

5. Kick the kickstarter crank.

Do not open the throttle while kick-
ing the kickstarter crank. Other-
wise, the kickstarter crank may
kick back.

6. Return the cold starter knob to its

original position and run the en-
gine at 3,000–5,000 r/min for 1 or
2 minutes.

Since this model is equipped with an
accelerator pump, if the engine is
raced (the throttle opened and
closed), the air/fuel mixture will be too
rich and the engine may stall. Also
unlike a two-stroke engine, this model
can idle.

Do not warm up the engine for ex-
tended periods of time.

STARTING A WARM ENGINE

Do not operate the cold starter knob
and throttle. Pull the hot starter lever
"1" and start the engine by kicking
the kickstarter crank forcefully with a
firm stroke. As soon as the engine
starts, release the hot starter lever to
close the air passage.

Restarting an engine after a fall

Pull the hot starter lever and start the
engine. As soon as the engine starts,
release the hot starter lever to close
the air passage.

The engine fails to start

Pull the hot starter lever all the way
out and while holding the lever, kick
the kickstarter crank 10 to 20 times to
clear the engine. Then, restart the en-
gine. Refer to "Restarting an engine
after a fall".

Observe the following break-in
procedures during initial operation
to ensure optimum performance
and avoid engine damage.

Recommended fuel:

Premium unleaded
gasoline only with a re-
search octane number
of 95 or higher.

Thrott

grip

oper-

ation*

Cold

start-

knob

Hot

start-
er le-