REFLECTOR: Re: Fuel Flow Sensor

[Chuck Harbert]

Kurt, I didn't know you had Don's injection system or my response would have 
been different. I had his 2 electric pump with bypass relief setup on my 
previous engine, and it returned fuel imediately to the pump inlet (all in 
the same package). I don't think there really should be fear of vapor lock 
with this arrangement, especially since it is outside the engine 
compartment.

Since all the fuel sent to the servo is used by the engine (similar to the 
normal Bendix A/C fuel injection system), you should be able to locate the 
floscan anywhere in the system (before or after the pumps). It should make 
no difference whether you push or pull fuel thru this device as long as your 
connections are air/gas light.

I need to pass on something that happened to me regarding my fuel system 
that I learned while test flying the plane a few months ago. Everything was 
operating fine until I tried to lean the engine in cruise. I have a 
helicopter (Bendix) servo on my plane which automatically adjust the fuel 
mixture for altitude and airflow, so as you climb it reduces the fuel flow, 
but always keeping the engine in a rich condition. I flew the plane several 
times and leaning was not a problem until after about 10 hrs total, but then 
when I leaned the engine would start to quit like it was running out of 
fuel. I'd imediately push the mixture to full rich and turn on the electric 
fuel pump, and the engine would run fine.

I checked everything (servo filter, fuel pressure, tightened fittings, etc) 
and everthing was per spec. I took a hard look at my fuel system and noticed 
that my (Fram Racing) fuel filter was above the fuel level in the wings 
(fuel comes from the sump tank then thru the filter then to the elec pump). 
When I took it apart it was half full of air inside which made me think the 
engine was drawing in air. I relocated it below the fuel level and haven't 
had the problem since. I should have known better than to not have a 
positive head on the suction side of the pump, but I learned a valuable 
lesson which fortunately didn't cost me.

Chuck H

------------------------------------