Husqvarna SM 50 / 2011, Workshop Manual

Page: 70 / 150

F.4
Ed. 01-09-2010
ENGINE
Valve opening - B
Operation with throttle valve during opening. Engine rpm is controlled by idle jet
and by valve shape. If, after idle speed correct adjustment and load reduction,
engine gallops, emits a lot of smoke and abruptly reaches full power at high
rpm when valve is opened, this means that carburetion is too rich, namely
that fuel level is too high, or that floater needle is not sealed.
Reduced load - C
Operation with throttle valve partially opened. Engine rpm is controlled by
taper needle only (shape and position). Reduced load operation and low
rpm are controlled by idle speed adjustment, while operation at high rpm
is controlled by main jet. If engine runs with a 4-stroke cycle or at reduced
power during acceleration with the throttle valve partially opened, needle shall
be lowered by one notch. If engine knocks, mainly during acceleration and
close to high rpm, needle shall be raised. If the above-described situations
occur at reduced load lower rpm, set a leaner mixture if engine gets wet, and
a richer mixture if it knocks.
Full load - D
Operation with valve fully opened. Engine rpm is controlled by main jet and
taper needle. If, after a short ride with fully opened throttles, the insulation of
a new spark plug is very clear or white, or if engine runs at 4 strokes, a larger
main jet shall be used; if lining is dark or darkened, use a smaller main jet.
Main jet
Taper needle
Taper needle
Idle jet
Valve
Idle speed adju-
ster screw