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4-3 Engine
4-3-6 Carburetor
At high altitude, the standard carburetor air-fuel mixture will be excessively rich. Output power will
decrease, and fuel consumption will increase.
Engine performance can be improved by installing a smaller diameter main fuel jet in the carbure-
tor and readjusting the pilot screw. If you always operate the engine at altitudes higher than sea
level 1000 meters over, have a Yamaha dealer perform this carburetor modification. If not, should
lower load power in operating gasoline engine.
Even equipped with suitable carburetor, engine horsepower will decrease approximately 3.5 % for
each 300 meter increase in altitude. The effect of altitude on horsepower will be lowered greater
than this if no carburetor modification is made.
NOTICE
If a carburetor suitable to high altitude is equipped with engine suitable to a lower altitude,
the lean air fuel mixture will make engine output power lowering, over-heat and seriously
damage.
The gasoline enters into the carburetor from the fuel tank and fuel filter. The fuel filter can filter the
foreign matters in the gasoline and oxide out of the fuel tank. If having quality defectiveness, partly
foreign matters will enter into the carburetor. Otherwise, the gasoline contains some composition
which can form the colloid after long sediment, and attach in the carburetor parts (such as main
jet) oil path and float chamber surface. The air enter into the carburetor through air filter, based on
the intake can not be too much resistance and other factors to consider, the filter can not be too
dense and therefore part of the air in the tiny impurities will enter into the carburetor through the
air cleaner.
Thermal baffle
Carburetor
Gasket
Stud M6 × 105
Thermal gasket
Gasket
Disassembly/reassembly:
First disassemble air cleaner, and disassemble the carburetor as shown on the above figure.
TIP
Before reassembling, check the carburetor thermal gasket, carburetor gasket, and air cleaner gas-
ket for damaged, please replace it if necessary. Please pay attention to assembling direction.
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