Fuel pressure mystery

Fuel vaporisation;

While always keeping an open mind I have my doubts about this line of thinking.

I have experienced fuel vaporisation, previous 912 ULS powered aircraft. It was a ground generated phenomena, which required very hot air temperature, a recently run (landed) engine, time for " heat soak" to occur, engine restarted (may have some difficulty) shortish taxi to run up bay/threshold & despite extended high power run up, loss of power shortly after (aborted) take off, followed by brief engine inspection, repeat TO this time with out problem.

What I am experiencing with this aircraft is; normal(4.5 psi) fuel pressure on ground, Dynon annunciating/showing low (less than 2 psi) pressure shortly after TO. At no time has the engine shown signs of fuel starvation/interruption.

Fuel type; As for the last 10-12 years of Rotax 9 operation, 100% 98 RON (ULP)

Sean, I know that fuel vaporization is a long shot, but minor fuel vaporization does not necessarily affect engine performance. The first sign can be a drop in fuel pressure, and may not progress further.  

I think you can rule out a fuel pressure gauge/sender problem since the pressure reading returns to normal if the boost pump is turned on.  So it would seem that the pressure is actually falling during the climb out, just not to the point where the engine performance is affected.  10 gallons of Avgas would be a cheap way to rule out a fuel vapor problem.  Good luck solving this, if you do it may help some others experiencing this same issue.  

Reporting in after .9 hr test flight -

Before TO, checked fuel pressure sensor has a small (about 1 - 1.5mm) hole in casing, to atmosphere - appeared to be clear.

After leveling out

Turned boost pump off, fuel pressure dropped to below 2 psi  - fuel pressure then returned to 4.5 psi & stayed there. This suggests to me that the pressure sensor may be taking time to "catch" up with change in air pressure.

After landing

Noted fuel pressure at 3500 rpm, about 4.5 -5psi

After shut down

Checked sample bottle on end of air box breather - about 15ml fuel. Seems I have a flooding/overflowing float chamber - will investigate .

Checked sample bottle end of pump drain - bit hard to see but might be empty  - will investigate .