Posted for Sky2high@aol.com:

 
 Pat,
 
 Interesting.......  There are at least two ways to create an over rich
 mixture. One, of course, is the way you mentioned - a system malfunction that
 
 supplies too much fuel for the selected operation mode.  In the case of a
 take-off, the throttle is positioned wide open (WOT), where special
enrichening  is
 used and imparting its full effect when max RPM is reached.   Closing the
 throttle somewhat takes the system out of the super-rich mode.   Note that
the
 problem would not be detected during run-up since that is not  usually
 accomplished at WOT.
 
 Another way is to partially restrict the induction air while  the throttle
 body is expecting more.  Suppose an interconnecting  induction hose partially
 collapses, a bird built a nest in the filter  compartment and/or the filter
 stops supplying enough air where alternate  air is not automatically
supplied,
 etc.  Again, this condition would not be  detected at any partial throttle
 setting such as run-up but would definitely  show up during take-off when
operating
 at WOT and max RPM.
 
 Keeping your mind on the paragraph just above, consider the setup where
 filtered alternate air is used for take-off by manually closing off
unfiltered
 ram air.  Consider that the filter is the highly regarded K&N.   Let's say
the
 filter was recently cleaned and re-oiled.  Let's further add  that too much
oil
 was used.  Finally, after some use, the dirt and oil  managed to close off
 the filter.
 
 OK, what stupid trick did I pull that made me think of an over oiled filter
 or restricted induction air?  Well, my fancy computer controlled motorcycle
 engine is run by sensing coolant temperature, OAT, MAP, RPM, exhaust O2 and
 throttle position.  It is equipped with a pricey polished one of a  kind ram
air
 induction port fed thru a rather small K&N filter.   About a week after I
 cleaned and re-oiled the filter, the bike began to run like  excrement -
black
 smoke, fits and starts, sputtering, etc.  Removing most  of the oil from the
 filter restored the pulsating power of 110 ci crammed into 2  jugs....
Ahhh....
 Anyway, the throttle position sensor led the computer to  expect just so much
 air - but no, the air wasn't there and the mixture  became too rich.  BTW,
 since no sensor failed its reasonable range test,  the computer did not think
 anything was wrong.
 
 Remember - Spark, Gas and Air are required for a burn.
 
 Scott Krueger  AKA Grayhawk
 Lancair N92EX IO320 SB 89/96
 Aurora, IL  (KARR)
 
 Abnegate Exigencies!