Rotax MMH-912 Series - 3.3.5) Diaphragm; 3.3.6) Jet needle

Effectivity 912/914 Series
Edition 1 / Rev. 3
page 27
October 01/2010
d04777
73-00-00
BRP-Powertrain
Maintenance Manual
3.3.5) Diaphragm
See Figs. 73-15 and 73-16.
The plunger (carburetor piston) (8) is attached to the diaphragm (6).
Depending on the pressure prevailing, the plunger is moved up or
down. For inspection, remove the two counter sunk screws (1) M5x12,
take off the chamber top (2) and remove the plunger spring (3). Check
that the cover plate (4) on the chamber top is tightly seated. Wash
chamber top with cleaning agent and blowclean the inside venting bore
with compressed air Then carry out a visual inspection.
Pull carburetor piston out of the carburetor housing and remove the 4
allen screws (5) M4x12. The diaphragm (6) is held by the retaining ring
(7) on the carburetor piston (8). The position of the carburetor piston
is controlled via the diaphragm. There are 2 indexing tabs on the
diaphragm (5). Tab (9) fits exactly into the recess in the slider piston and
nose (10) must engage in the recess in the carburetor housing.
Check diaphragm for cracks or brittleness, replace if necessary.
3.3.6) Needle
See Fig. 73-16.
The needle (12) controls the fuel consumption at part load. It can be
regulated by selecting a needle position between 1 and 4.
Unscrew the retaining screw (11), check needle (12) with shaft securing
(13) and O-Ring (20) for signs of wear.
Pay especial attention to the grooves and the taper of the needle. If
there is visible wear, the needle must be replaced and a new one refitted
in the same position. The needle jet must be replaced along with the
needle as it will also be worn.
◆ NOTE: The needle must move freely when fitted.
Carry out a visual inspection of the outer diameter of the carburetor
piston (8) and the two inside compensation bores.
◆ NOTE: The needle is damped by the O-ring (38).
See Figs. 73-13 and 73-14.
The set up of the needle position (Fig. 73-15/1) and the determination
of the main jet should to be carried out in accordance with the table of
Fig. 73-15/2. The settings have to be recorded in appendix chapter 8.2
“carburetor jetting and jet needle position”.