Posted for Berni <bbreen@cableone.net>:

 We have seen this problem repeatedly even following refueling from several
different airports. I guess this would negate the possibility of the cause
being a difference in fuel(?).
 
 Your comment regarding the air is interesting.  I don't believe we have any
air in any of the fuel lines but maybe I should look harder at this
possibility.
 
 Thanks for your input.
 
 Sent from my iPad
 Berni Breen
 Bbreen@cableone.net

[Related, sort of... some years ago Gene Underland (rest his soul, I still miss him) flew in with his ES to visit while I was working on Ted Noel's IVP at the Deland airport.  It was a hot summer day, Gene had flown a short distance from the gulf coast, and was parked on the ramp in front of the hangar for about 90 minutes.  When he went to leave he was unable to start the engine (IO550) due to cavitation of the boost pump (mounted on the engine side of the firewall).  Apparently the under-cowl heat was great enough to boil off the fuel in the pump and it simply wouldn't draw up from the wings since it was trying to pump vapor.  We got him started by hooking an air line to his wing vent and slightly pressurizing the wing, forcing liquid fuel up to the pump.  He'd suffered the problem before and we discussed and solved it by installing a small Facet pump at the wing root that he would actuate prior to running the boost pump when starting after a brief shutdown.  It would purge the vapor and allow the boost pump to do its job.  I realize this doesn't solve a similar in-flight issue but it does highlight the value of both pushing fuel instead of drawing it, and the importance of keeping temperature sensitive fuel components cool enough to do their jobs.  Just shared as a data point....   <Marv>    ]
 
 
 On Jun 17, 2011, at 12:46 PM, "Steve Colwell" <mcmess1919@yahoo.com> wrote:
 
> The problem could be a slight change in the initial boiling point of 100LL.
> The specs for 100LL may allow refiners to vary just enough to cause fuel to
>start to bubble in the lines at a temperature and density altitude that was OK
>previously.  The boost pump would solve this problem most of the time with
>100LL; with auto fuel, maybe not.
>
> About leaks.  Fuel has lower surface tension than air so it will leak when
>air won’t.  I learned this when air trapped in a fine screen Gascolator with a
>glass bowl in an Aircoupe.  Fuel would pass thru the screen but the air bubble
>in the top would not!
>
>  
>
> Steve   Legacy
>
>  
>
>  
>
> At 6,500’ the engine began surging.  When we turned the auxiliary fuel pump
>on the engine immediately ran fine.  We have now had the engine driven pump
>overhauled.  We have pulled vacuum through the entire fuel system and we have
>no leaks.  We replaced 100% of the flexible fuel lines.  Metered and
>un-metered fuel pressures are reset and fine.  We are at a loss as to what is
>causing our engine surging problem.
>
>  
>
> Berni  
>
>  
>
>  
>
>  
>
>  
>
>