Pro Boat PRB2700 - Manual (Page 10)

10
Model engines run on a mixture of fuel and air. The
high-speed and low-speed needle valves control
the ratio of fuel to air that the engine receives. If
you find that small adjustments are needed, have
an experienced modeler help you to fine-tune your
engine. Do not attempt to move the needles past
the preset stops.
High-Speed
Needle Adjustment Low-Speed
Needle Adjustment
Warning: Make all adjustments
to the Evolution engine’s low-
speed needle valve with the engine
stopped.
Our technicians have preset the needle valves
of the Evolution engine. Your engine should run
properly at these preset needle settings. On
occasion, depending on your location, you may
find it necessary to adjust the high-speed and low-
speed needle valves to optimize the performance
of your engine. The needle valves have limiters to
allow small adjustments to the engine. The low-
speed needle valve limiter allows 1/4 turn of the
needle valve, turning clockwise (in) will lean the
mixture while turning counterclockwise (out) will
richen the mixture to the low-speed or idle setting
of the engine. The high-speed needle valve limiter
allows one full turn of the needle valve. As with
the low-speed adjustment, turning the high-speed
needle valve clockwise (in) will lean the mixture,
while turning counterclockwise (out) will richen the
mixture of the high-speed setting of the engine.
Fine-Tuning the High-Speed Needle
Start your engine and advance the throttle to full,
then pinch the fuel line going to the engine. If the
engine dies immediately without an increase in rpm,
the setting is too lean. Adjust the high-speed needle
valve counterclockwise (out) 1/2 turn and repeat
the test. When the high-speed needle is adjusted
correctly, the engine should increase rpm slightly
and then quit. If the engine rpm increases more than
200–300 rpm and continues to run, the needle valve
setting is too rich. Adjust the needle valve clockwise
(in) 1/8th of a turn and repeat the test until the
engine responds correctly to the pinch test.
Fine-Tuning the Low-Speed Needle
After fine-tuning the high-speed needle, you can
begin to test the low-speed needle. Start your
engine and go to full throttle for approximately
5–10 seconds then return to idle. Pinch the fuel line
going to the engine. If the engine dies immediately
without an increase in rpm, the setting is too lean.
Adjust the needle valve counterclockwise (out)
1/8th of a turn and repeat the test. When the
low-speed needle is adjusted correctly, the engine
should increase rpm slightly and then quit. If the
engine rpm increases more than 200–300 rpm and
continues to run, the needle-valve setting is too
rich. Adjust the needle valve clockwise (in) 1/16th of
a turn and repeat the test until the engine responds
correctly to the pinch test.
Section 7: Engine Adjustments