Troubleshooting - Yamaha BR250F Service Manual

1. Main jet
G. Troubleshooting
WARNING:
Never remove the main jet cover bolt while
the engine is hot. Fuel will flow out of the
float chamber which could ignite and cause
damage to the snowmobile and possible injury
to the mechanic.
Place a rag under the carburetor so fuel does
not spread. Place the main jet cover bolt in a
clean place. Keep it away from fire. After
assembling the carburetor, firmly tighten the
rubber joint screw. Make sure the throttle
outer tube is in place and the throttle cable
moves smoothly. Clean the carburetor and
allow it to dry.
Trouble Check point Remedy Adjustment
Hard starting Insufficient fuel Add gasoline
Excessive use of starter
Clean spark plug
Return starter lever to its seated
(Excessively opened choke) position.
Fuel passage is clogged or Clean Parts other than carburetor
frozen
• Clogged fuel tank air vent, clogg-
ed fuel filter, or clogged fuel
passage
Carburetor
• Clogged or frozen air vent clogged
valve.
• If
water collects in float chamber,
clean.
(Also check for ice.l
Overflow Correct
Poor idling
Improper idling speed
Tighten slow adjuster lightly, and
adjustment check throttle opening. If incorrect,
(Relative troubles) • Slow adjuster Adjust idling speed back it out specification. Start the
• Poor performance at low engine and turn slow adjuster in
speeds and out 1/4 turn each time. When
• Poor acceleration
the engine runs faster, back out
• Slow response to throttle throttle stop screw so the engine
• Engine tends to stall idles at specified speed.
• Throttle stop screw Adjust
Tightened to much - Engine speed
is higher.
Backed out too much
Engine
does not idle.
Damaged slow adjuster Replace slow adjuster
Clogged bypass hole Clean
Clogged or loose slow jet
Clean and retighten Remove slow jet, and blow it out
with compressed air.
Air leaking into carburetor Retighten band screw
joint
Defective starter valve seat
Clean or replace
Overflow Correct
Poor performance at Clogged or loose slow jet Clean and retighten
Remove slow jet, and blow it out
mid-range speeds
with compressed air.
(Relative troubles)
• Momentary slow response
to throttle
• Poor acceleration Lean mixtures
Overhaul carburetor
3-7