PA32-260 Auto Fuel STC

I know anecdotally from my IA that some of the Cherokees are somewhat
marginal in their ability to handle the high vapor pressures of winter
autofuel. They would stumble on takeoff & climbout the first hot days
of spring.

The symptoms that I had heard sounded more like flooding rather than
fuel starvation. It could be that the floats were sinking in the carb
bowl as the fuel was boiling. The front of the bowl is close to very
hot exhaust pipes, and the bowl vent is back directly into the air
intake. Any one else know any more than this?

I had heard some of the Grummans have had the autofuel STC pulled for
similar reasons.

Those of us using the autofuel STCs have to be cognizant of its
possible limitations. It has worked well so far in my 172M (about 15
years), but I avoid flying in very hot weather and avoid parking bright
sun (being concerned about fuel tank heating) just on principle. I'll
let someone else verify that experiment.

Pilots talk about the vapor pressure as though it is an absolute
measure. It is not as it doubles about every 15 degreesF. Raising a
fuel temp 15 degrees F will increase the actual vapor pressure of avgas
enough to eliminate the measured reduced pressure benefit of avgas. In
other words, autofuel has a 15 deg F handicap in handling high fuel
temps.

Octane requirements are a separate issue. The 235 HP Cherokee is an 80
octane engine, the 260 requires higher octane than regular.
(Petersen is no relation to me)