BRP ski-doo MACH Z 1000 SDI, Handbook

Page: 142 / 493

05-18
MMC2005-001_05A.FM
SECTION 05 - ENGINE PREPARATION
Carburetor Test
Once the aperture of the carburetor is determined,
a test to select the proper jet should be made. The
size of the jet is determined by measuring the out-
put in a bench or in a chassis dynamo test. For
racing, it is best to determine the proper size of
the jet on the racing track, because the following
points must be taken into account:
a. The altitude (atmospheric pressure), temper-
ature and humidity of the race track.
b. The operation of the engine based on the to-
pography of the race track.
Pilot/Air System
PRINCIPLES OF OPERATION
The pilot/air system controls the fuel mixture be-
tween idle and approximately the 1/4 throttle po-
sition. As the throttle is opened wider for low speed
operation, the pilot outlet cannot supply adequate
fuel, and fuel then enters the carburetor bore from
the bypass as well as the pilot outlet. The pilot/air
system is tuned by first adjusting the air screw;
then, if necessary, by replacing the pilot jet.
Adjusting Air Screw
1. Pilot bypass
2. Pilot outlet
3. Pilot jet
4. Air intake
5. Air screw
NOTE: This procedure may be performed for sin-
gle and dual carburetors. Never adjust screws
more than 1/4 turn at a time.
1. Turn idle stop screw in until screw contacts
throttle valve. Then turn idle stop screw in 2 ad-
ditional turns.
2. Start and warm up engine. Adjust idle stop
screw to 500 RPM above normal idle speed.
See
Low-Speed Fuel System .
3. Turn air screw in or out using 1/4-turn incre-
ments until engine RPM peaks or reaches its
maximum RPM.
4. Readjust idle stop screw to return engine to nor-
mal idle speed. See pages Low-Speed Fuel
System .
5. Repeat Steps 3 and 4 until engine operates at
normal idle speed and air screw is peaked.
6. When air screw is adjusted stop engine. Note
the setting of air screw and turn it all the way
in. If it takes less than 1 turn, the pilot jet is too
small and a larger one must be installed. If it
takes more than 2-1/2 turns to set air screw, the
pilot jet is too large and must be replaced by a
smaller one.
7. Turn the air screw left and right (between 1/4
and 1/2 turn) and select the position where the
engine revolution reaches the maximum. Adjust
the throttle stop screw to bring down the engine
revolution to your target speed for idling. After
this adjustment of the throttle stop screw is
made, select once more the position where the
engine revolution reaches the maximum, by
turning the air screw left and right (between 1/4
and 1/2 alternately). At this point, attention
should be paid to the following points.
a. If there is a certain range in the opening of
the air screw where the fast engine revolu-
tion can be obtained (for instance, the num-
ber of revolutions does not change in the
range of 1-1/2 to 2.0 turns), it would be better
for acceleration to 1-1/2 turns.
5
A01C4FA
4
1
2
3