Posted for Dr Andre Katz <bu131@swbell.net>:

 you forgot one more factor in the myriad of answers, the duke's fuel pump is
located inside the cockpit, therefore is pressurized, pressurization in a IV-P
has a factor in the fuel flow, in my IV-P I believe its the reason for the
acute engine power loss when shifting tanks, the only way to avoid it is to go
high in the boost prior to switching, if you get a leak in the fuel pump like
it occurred to me you loose pressure. This event never happens at low
altitude, therefor my small brain tells me it pressure related. One more thing
to consider.
  andres
 
"""
 John Hafen <j.hafen@comcast.net> wrote:
                I would like to thank all those who responded to my question
about when to turn on the fuel boost pump when flying a Lancair IVP.

  Based on info gleaned from the posts, it appears that the answer is
“whenever it is necessary depending on your specific plane.”  As some never
use their boost pump after engine start, others turn it on for take off,
others turn it on at 3k feet or 6k feet or 10k feet or after reaching cruise
at 24k feet, it appears that there is no dependably consistent answer that
would apply to every plane, even in identical environments (temperature,
pressure etc).  We are left to figure it out on our own.  But at least I know
a little bit about why, thanks to your feedback.
"""