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Is This A Good Practice or Not??

todehnal

Well Known Member
Following each flight, I use a shut down procedure that includes closing the fuel valve until the fuel pressure drops low enough for our warning girl to offer a gentle reminder, then shut down. This only takes about 20 seconds. The idea is to reduce the fuel level in the 2 carbs so that the fuel expansion created by the engine compartment heat will not cause carb bowl overflow. I did consider the fact that the fuel pump is running dry, but I can't imagine that this is an issue. The next start is preceded by running the electric pump until fuel pressure is satisfactory before doing a start. Everything seems to be going fine with this practice, so far, but I thought this might be worth a question to the forum.

Thanks for your thoughts.......Tom
 
I haven't been doing that and, as far as I know, the carbs haven't had an overflow. Might have been happening but I haven't seen any evidence of it. Don't know as it would do any harm, tho.
 
A while back, I posed a similar question on the Rotax-Owners' website. The Rotax-Owner rep responded that he could not see any real value to running the carb bowls dry (or low) during engine shut-down. He expressed some concern regarding the suction pressures impacting the engine-driven fuel pump.

In the end, I decided to just leave my in-cockpit fuel valve ON basically all of the time. I have seen no evidence of fuel bowl overflow due to heat-related fuel expansion.

Your proposed procedure sounds OK to me. It also may have the benefit of unporting the needle valves and allowing any sediment therein to fall to the bottom of the bowl?

ps -- Some users prefer to shut OFF the fuel valve after engine shut-down to minimize any subsequent leakage in the gascolator and/or forward fuel lines due to a sudden component failure. However, such an occurence seems unlikely to me. I am more concerned with wear and tear on the valve and the potential for accidently kicking the fuel valve actuating lever. YMMV
 
For those of us with older engines (mine is a Continental C85), particularly those with Stromberg carbs, shutting the fuel off and running the engine dry is standard operating procedure. These old low-compression engines are prone to firing when the prop is moved inadvertently, so running the carb dry is a good safety enhancement.

Fast forward to the RV12 with its electric fuel pump and I'm not sure how advisable it is to run the fuel pump dry. The typical Facet pumps don't like being dry. It might be a good idea to research how your pump behaves with being run dry. Investing in a spare pump with which to conduct your own empirical testing might, in the long run, be a very wise thing to do.
 
I wouldn't use this method because of the number of cycles it puts on the fuel valve. The more you cycle it, the more chance of developing a stem leak. I had that problem on my Cherokee fuel selector valve.
 
For those of us with older engines (mine is a Continental C85), particularly those with Stromberg carbs, shutting the fuel off and running the engine dry is standard operating procedure. These old low-compression engines are prone to firing when the prop is moved inadvertently, so running the carb dry is a good safety enhancement.

Fast forward to the RV12 with its electric fuel pump and I'm not sure how advisable it is to run the fuel pump dry. The typical Facet pumps don't like being dry. It might be a good idea to research how your pump behaves with being run dry. Investing in a spare pump with which to conduct your own empirical testing might, in the long run, be a very wise thing to do.

Mark, I think that you found the source for my concerns. I was, indeed, a PA-11 Cub driver before we built out 12. It was C90 dash 8 powered, and had the carb issues that you mentioned, and hot props were always a worry. I think that you guys have convinced me to move into the modern world, and to use the fuel system as it was intended. I will monitor for post flight fuel odors and go from there.............Tom
 
As a minor technical note, it is not the FACET electric pump that I would worry about (a closed fuel valve would not cause the FACET pump to run dry any more than a stopped engine would - other than a slight return flow to the fuel tank). It is the engine-driven ROTAX mechanical pump that would run dry and perhaps build up some potentially damaging pressures (pressure or suction?). I recall hearing that the FACET pump should not be run dry for prolonged periods due to the absence of fuel for cooling and lubrication.
 
It's not a good practice. This isn't a Cont. or Lycoming engine. Turn the engine off and then the fuel is all that is needed.
 
Spare fuel pump

As a minor technical note, it is not the FACET electric pump that I would worry about (a closed fuel valve would not cause the FACET pump to run dry any more than a stopped engine would - other than a slight return flow to the fuel tank). It is the engine-driven ROTAX mechanical pump that would run dry and perhaps build up some potentially damaging pressures (pressure or suction?). I recall hearing that the FACET pump should not be run dry for prolonged periods due to the absence of fuel for cooling and lubrication.
Should one carry a spare mechanical pump or the electric one?
 
Personally, I carry a spare ELECTRIC fuel pump in my RV-12. My spare electric pump has the two special AN fittings and electrical connectors already installed to facilitate a quick field replacement -- hopefully never to be needed! My RV-12's ROTAX has the newest style of ENGINE-DRIVEN fuel pump (some 5+ years old now) and they seem to be relatively reliable over time. I do not carry a spare engine-driven pump.

As part of my pre-flight before each flight, I take a close look at the drain tubes for both the oil tank (breather) and engine-driven fuel pump. Typically, there is a drop or two of oil at the exit point of each tube -- I consider this normal and it has been that way for 500+ hours. I am amazed at how clean my engine is after 500+ hours -- nary a drop of leaked fluid anywhere firewall forward. :)
 
The old engine driven fuel pumps were not reliable but the new ones have a good track record. So I would skip buying one as a backup. Buy a voltage regulator instead. ;)
 
The old engine driven fuel pumps were not reliable but the new ones have a good track record. So I would skip buying one as a backup. Buy a voltage regulator instead. ;)

Both are available at your local NAPA auto parts store. No need to lug either of them around.
 
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