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  #1  
Old 06-10-2016, 10:22 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
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Default Is This A Good Practice or Not??

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
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  #2  
Old 06-10-2016, 11:00 AM
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tomkk tomkk is offline
 
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Location: Port Orange, Fl
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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.
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  #3  
Old 06-10-2016, 11:26 AM
DHeal DHeal is offline
 
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Location: Windsor, California
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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
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EAA #23982 - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B) - N124DH flying since March 2014 - 700+ hours (as of Nov 2018)!
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  #4  
Old 06-10-2016, 11:29 AM
Canadian_JOY Canadian_JOY is offline
 
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Location: Ontario, Canada
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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.
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  #5  
Old 06-10-2016, 12:33 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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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.
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  #6  
Old 06-10-2016, 12:38 PM
todehnal todehnal is offline
 
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Location: Kentucky Lakes area in KY
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Quote:
Originally Posted by Canadian_JOY View Post
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
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1989- RV-6 tail kit, built and sold
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  #7  
Old 06-10-2016, 01:29 PM
DHeal DHeal is offline
 
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Location: Windsor, California
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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.
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David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B) - N124DH flying since March 2014 - 700+ hours (as of Nov 2018)!
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  #8  
Old 06-14-2016, 09:22 AM
Sink Sink is offline
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Location: Altha, FL.
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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.
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  #9  
Old 06-16-2016, 11:49 AM
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Bill_H Bill_H is offline
 
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Location: Peel, AR
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I never touch the fuel shut-off valve except at the condition inspection.
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  #10  
Old 06-21-2017, 04:56 AM
AirHound AirHound is offline
 
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Location: OFallon IL now, everywhere before
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Default Spare fuel pump

Quote:
Originally Posted by DHeal View Post
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?
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