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JETTING YOUR CARBURETTOR
JETTING YOUR CARBURETTOR FOR:
• BEST PERFORMANCE
• CORRECT ENGINE TEMPERATURE
(Cylinder head 230~240°C)
• INCREASED ENGINE LIFE
ADJUSTING YOUR IDLE SPEED:
ENGINE IDLE SPEED - 2,000RPM
• Increase Idle Speed:
Using a screwdriver, turn clockwise
• Decrease Idle Speed:
Using a screwdriver, turn anti-clockwise
FROM THE FACTORY: The carburettor is supplied with Main Jet
96 - Pilot Jet 45. In many cases, this would be considered as a rich
setting but is done to protect against running the engine too lean
straight out of the box.
AS A STARTING POINT, in areas less than 300m above sea level
and with temperatures above 20°C, we suggest starting with a 94
Main Jet and a 40 Pilot Jet.
The carburettor mixes fuel and air at a precise ratio, before it goes into the engine to be burnt.
When the fuel air mixture is correct, the engine performs at its best. However this precise fuel air ratio is affected by a
number of outside influences, most significantly – altitude (air pressure) and temperature, but is also affected to a lesser
degree by humidity.
The factory supplied jetting is a starting point only; for optimum performance you will need to read the spark plug and
engine temperature under track conditions to determine the optimum jet sizing required.
Racing on tracks that are more than 300 meters above sea level, or in a different temperature range (+ - 10°C), requires
that you re-jet your carburettor to compensate.
Going higher results in lower air pressure (lower air density). When racing at higher elevations your engine is getting
less air, so it needs less fuel (a smaller jet) in order to maintain the correct fuel/air ratio. Under such conditions your
horsepower will also go down, this is both unavoidable and universal for all competitors, you can figure on losing about
3% of your engine power for every 300m (1000 ft) of elevation.
Now if overnight it gets really COLD! You should also be thinking about re-jetting again! Cold air is dense air, and dense
air requires more fuel (a bigger jet). The jet you won the race with yesterday afternoon (when it was hot), will be too lean
now, you need a bigger jet to run properly when it’s cold. Air temperature makes that much difference! If the temperature
is just 10 degrees colder than it was when last you raced, then you risk damaging the engine by running too lean, if you
don’t change to a larger main jet.
The Main Jet; is the most critical for ensuring full power operation, correct engine temperature and thereby a long engine
life.
The Pilot jet and the low-speed idle mixture screw; work together, the pilot jet controls the amount of fuel available and
the low-speed idle mixture screw allows you to precisely control the idle mixture being allowed into the engine at idle.
CHOKE LEVER:
The choke lever opens and closes the
choke valve in the carburetor.
• Move the choke lever into the
START position for starting.
• After starting, slowly move the
choke lever to the RUN position.
START
RUN
