"Bob Olds" wrote in message
om...

I use a mixture of 100LL and mogas. My RV-4 sat in the sun all day
with temp. 95 F. As I taxied I noticed a miss now & then,so I turned
on the electric boost pump and had no further problem in the flight.
My boost pump is located beside the fuel selector valve,at the lowest
point possible.
The engine driven pump makes suction in the fuel line from the valve
to the pump. With a suction/vacuum the boiling point is lowered =
vapor lock.
With a boost pump in the engine compartment, you add another hot place
for the fuel to boil.
I have had the same problems with 80 oct.,100LL and mogas. They are
all problems when the tank gets so hot.

Bob Olds RV-4 , N1191X

Bob.............

Your recommendations to prevent vapor lock are sound. However, unless you
have tested the system under actual extreme conditions, it is best to not
trust it. 100 LL (much as I hate its cost and tendency to foul plugs) is
more resistant to vapor lock than mogas. Especially mogas out of a tank at
an airport which may be last Winter's blend.

Rich S.