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DIRT IN CARB Every now and then, when you can't
get an engine to run right, the culprit is
dirt in the carburetor. The engine was
running fine last time out, and you
haven't changed the engine settings.
Now it quits at full power and won't
idle. What's wrong?
If you haven't been to the field in
six months, make sure you're using fresh
fuel! Fuel that's been sitting around for
months, especially if it's left in the fuel
tank, could be your problem. If it's not
the fuel, put in a new glow plug. Check
the clunk hung up in the fuel tank for
clogged fuel lines. If your aircraft
comes to a sudden stop, the fuel tank
clunk can slide forward, getting stuck in
that position.
Having eliminated these possibilities,
you may have a fuel draw problem
caused by dirt in the carburetor, most
likely at the narrowest part where fuel
is drawn through the needle valve. If
backing out the needle valve doesn't
allow the engine to run rich like it
should, it's time to flush the carburetor.
At home, you can disassemble the
carburetor for complete cleaning. At
the field, a quick fix is to back flush the
carburetor with fuel. This doesn't
require carburetor removal and can be
done in just a few minutes.
Cleaning the carburetor
1) Check to see where the main
needle valve is set. Then remove it and
set it aside. Remove the fuel inlet
tubing. Adapt these procedures to
engines with remote needle valves.
2) Connect the fuel tubing from
your fuel pump to the fuel inlet nipple.
Pump fuel. It's a bit messy but only
takes a second or so. Almost invariably,
the culprit is a particle of dirt lodged at
the point where the tip of the needle
valve throttles engine fuel. The back
flush blows that particle out.
3) You've probably got excess fuel in
the engine. To avoid hydraulic lock
damage to your engine, remove the
glow plug and washer and blow the
excess fuel out of the engine with your
electric starter.
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