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I just changed my 4P fuel selector to the Andair because of the following
stories. My plane is due to fly by the end of next month (Hope, Hope) and a
friend who just flew his 2 months ago went through several engine stoppages
before changing to the Andair which is what the factory now sells. It cost me
$500.00 more and I have a brand new old type for sale.
This friend found that by purging both tank positions before take off that it
helped the original fuel interruption problem until he flew at high altitude
for over 1 hr. and then, even with the purge before flight, the engine
stopped for 20 seconds (seamed like forever, he said) when switching tanks.

His theory(and several of us agree) is that when the selector was feeding
from one tank the Cabin Pressure was pushing air into the Unselected tank
line inside the Selector Valve. Upon changing to the Andair the problem went
away.
I also flew to OSH last month in another 4P that has over 570 hrs. TT and I
discussed this fuel problem with the owner /builder. He said he never had a
problem but he had changed out the very first selector he got with his kit in
92/93. So as we are flying at FL220 and switching tanks after 20 gals burned,
the engine stumbled. He said that he may need to look into that stumble.

I changed mine because I feel that fuel flow is a MUST HAVE item.
To change form the last generation factory selector to the Andair (current
factory selector) is Not a trivial issue. It requires some new bent lines and
new fittings. While I was at it I moved my boost pump to the lowest position
under the right floor foot rest and made sure the flex line from the wing to
the fuselage is laying as low / horizontal as possible all because if you do
get air pushed into the line, from the selector side, it could cause an
airlock at the high point in the line TO the boost pump. Since the pump is
Not a self priming pump, it needs fuel to pump not air. I don't know if the
tank vent line gets pressure from the small NACA scoop on the tip but that
and gravity would be the only way to push the air through the pump. I also
installed 1/2 in. line from tank to selector even though this may not be a
real necessity.

How may others have had a fuel flow interruption issue with the 4P?

Jim Hergert
L4P in paint.
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Please send your photos and drawings to marvkaye@olsusa.com.
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