| Fuel
Contamination Advisory - July 23, 2004
The following is an overview of a recent experience that I personally went
through in preparation
of getting my Chinook 912 ready for its first test flight with the
new ASAP Retract gear.
During the week of July 12, we installed the new
ASAP retract for the Full Lotus floats on my Chinook 912. The airplane
had been sitting in our hangar for about 9 months. It had normal
mo-gas in the tanks. We finished the installation and rolled the
airplane out to do a complete and thorough engine run-up. From past
experience I know that the gas will have deteriorated to the point
that it required draining, but I decided since I was just going to do
a static run-up that I would just use what was in the tanks. The
engine started but of course ran rough, it would idle and then during
the application of RPM it would stumble and then catch after a certain
amount of throttle movement. So I decided to switch tanks and
after a minute or so the engine completely quit. So I said that’s
it, enough is enough lets roll it in and go through the fuel system.
The first thing I did was pull out the pick-ups
in the strut mount fuel tanks (part # 12-16’s), I gave them both
a shake, one was loose and free and one was stuck. So found out
the cause as to why I had the engine quit on that one fuel tank.
As it states in our owner’s operator’s manual,
the pick-ups
are to be changed Every 50 hours...(click
here) or 4 weeks. ( Please note that we
have moved this out of the 100 hour section into the 50 hour and
also put a 4-week notation as well.) I then changed both pick-ups and fuel lines
inside the tank. Note: the grade of gas can greatly reduce or
increase the life of fuel line, fuel filter, screens etc etc. For
example if one was to use AV gas there have been reports of AV gas
being used for a year or longer, however there is even a notation
to this statement and that is dependant on climate, which will
once again affect the above mentioned items. Water and UV
being two of the more notable culprits.
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It
is easy to check these by unscrewing the pick-up tube
inspecting the one-way valve. |
After
filling the tanks with new
fuel I noticed I had one drain valve leaking, so I drained
the fuel and unscrewed the drain valve, you can see the
condition of the drain valve in the photo. I also replaced
the fuel filter which was also contaminated.
| After
filling the tanks with new fuel I noticed I had one drain valve
leaking, so I drained the fuel and unscrewed the
drain valve, you can see the condition of the drain
valve in the photo. I also replaced the fuel filter
which was also contaminated. |
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So
with new items (as noted above) and new fuel installed I
once again pushed the airplane out and tied up the tail and
proceeded to do a full power run-up. The idle was noticeably
improved but I still had a hesitation from idle to full
power. I switched tanks and the problem still existed so once again I pushed the airplane back in the
hangar and said I will work on the airplane first thing
Monday.Saturday
and Sunday were extremely nice days and it would have been a
great day to go flying but also not having an airplane 100%
healthy was and always is a no go for me!
Monday
morning I removed the carbs and found the reason for my mid
range hesitation. As you can see by the photo the jet needle
was fully engaged with spent fuel residue. Seeing the needle
in this condition I decided to disassemble the complete carb.
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