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Valach VM 120 B2-4T Instructions
9
Carburetor
The loosely supplied intake RAM tube , has to be mounted to the engine in any
case! Without it, the engine runs too lean, also with wider opened jet needles!
The correct tuning of the engine can only be achieved, with a mounted intake RAM
tube. The intake tube saves fuel and keeps the model under the cowling cleaner. It is
not attached on the delivered engine, only for transportation reasons.
A pre adjusted Walbro carburetor with two jet needles ( L: low speed needle and H:
high speed needle) is mounted on the engine. The low speed needle influences the
throttle response from idle to about 40% of the maximum RPM.
The
basic adjustment
for the high speed needle is 2 turns open (screw the needles
carefully in and screw them out two turns) and 1 3/4 turns for the low speed needle.
The fine-tuning for best performance and throttle response is made after the engine
is mounted in the model.
On my engine, after breaking-in the high speed needle is 1 1/2 turns and the low speed
needle 1 1/4 turns open.
The diaphragm pump into the carburetor is supplied with the pulsing crankcase
pressure by a tube. Keep an eye on the condition of this tube, because it is essential
for the correct functioning of the engine. You can read detailed instruction under
“Maintenance”.
Hint:
Adjust the response time of your throttle servo in your transmitter to 1 sec. from idle
to full throttle. Other than expected, the throttle response will be faster and of course
more reliable, especially from low idle. The response time from full throttle to idle can
be on full servo speed.
Low speed needle High speed needle
The intake RAM tube is
absolutely necessary!
Without it, the engine will
run too lean.
Idle block screw, remove
after test bench runs..
Tube for the pressure
supply of the pump into
the carburator.
