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Push or Pull?

Eustace Bowhay on Fuel Injection vs. Carburettors

Eustace Bowhay (
Blind Bay, BC

Iíd like to pass on my experience with fuel systems over the years and as related to my RV-6.

All of my flying with horizontally opposed engines since the sixties had been with fuel injection until my RV-6.  At the time of building the -6 I didnít think I had a choice, with Van recommending only the O-320 and O-360 Lycomings.

My choice was the O-360.  With most of our flying here over hostile terrain and sparsely settled areas, I decided to install the Gem graphic display.  This would give me advance warning of any valve problems, as well as mixture and ignition info.  This is when the wide spread in mixture to the four cylinders showed up, and having to lean to the leanest cylinder wasnít the really the most efficient .

Carb icing was a bit of a concern, with the difficulty of getting what I felt was adequate hot air for carb heat.  Turned out to be a non issue, with the crossover exhaust system located over the alternate air door.

I had my engine overhauled in 1996, and decided to give the Bendix Fuel Injection a tryóa system I was familiar with.  This is a big change, requiring a change in both the engine driven pump and the boost pump, because of the higher pressure  and the extra plumbing required.  This was another reason for moving the gascolator into the wing root (so that the gascolator would not be pressurized).  I mounted the Weldon pump on the fuselage side of the firewall above the rudder pedals.  That wasnít ideal, because of the lift, but didnít want it in the engine compartment because of the heat and starting problems associated with fuel injection on short turnarounds.  This problem was completely solved with the installation of a AirFlow Performance purge valve this year.

 Flying with the fuel injection system is a real treat, to see the EGTs straight across, and the CHTs almost the same.  The leaning is now the same on all four cylinders.  Carb ice is a thing of the past.

So which system is the best ?  Here again I think it is a matter of personal choice.  Cost is certainly a major factor with fuel injection.  I believe fuel injection is more reliable but can honestly say I havenít had any trouble with either.  Itís hard to beat the simplicity of the carb system, and in my opinion a carb gives easier all around starting with less wear and tear on the starter and battery.  However, fuel injection has to be better for the engine because of itís even fuel distribution and better leaning, and has the added benefit of no carb icing problems.

I am looking seriously at the Airflow Performance system for the -6A because of the pump ($300 versus $1000) and the purge valve.  It uses a large capacity inline filter (I believe between the pump and the throttle body) that I would like to know a bit more about.  Iíll also use the Andair gascolator  for itís better quality and easier servicing.

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