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Tristan

You mentioned that you do not have a header tank and that you have a fuel
selector that has positions for R - L - Both and off.  A both position in a
low wing aircraft is considered dangerous by the FAA and not allowed in a
certified low wing aircraft because if one tank unports or runs dry before the
other one the fuel pumps would suck air even though fuel is present at the
other port.  I have been flying a Lancair 290 for some 7 years without a
header tank and  do not have a both position on my selector for this reason.

Another problem I encountered while testing was that I originally had the
electric fuel pump installed after the Gasgolator like the manual shows and I
ran into some funny problems.  First I experienced what appeared to be vapor
lock.  Second the primer would not work right because it would not fill up all
of the way because there was no pressure at the input to the Gasgolator ( No
Header Tank)   After checking around I found that with a low wing and no
header tank the electric pump needed to be installed before the Gasgolator to
pressurize the gasgolator.  I changed mine by installing it in the cabin on
the fire wall.  It now stays cool (no Vapor Lock Problem) and the primer works
fine.  Now that I am building a Lancair IV I found that thats how they do it
too.  Please consider changing your fuel selector to a R-L and off only or at
least Placard to not use both for take off and landing or when the fuel level
is below about 7 or 8 gal in either tank.

Regards Tom Byrnes N133TB