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fuel leak or auxiliary fuel pump malfunction?
From time to time pilots have observed fuel stains on the nosewheel
wheelpant of our club's 172SP. The only time I have actually seen fuel dripping from the engine was when I watched a pilot turn the auxiliary fuel pump on for what seemed to me to be an excessively long period of time. The fuel appeared to be dripping out of one of the two plastic hoses that come down through the cowling just ahead of the firewall. I have assumed that the cure is to prime the engine according to the POH: 5. Auxiliary Fuel Pump Switch -- ON. 6. Misture -- ADVANCE until fuel flow just starts to rise, then return to IDLE CUT OFF position. 7. Auxiliary Fuel Pump -- OFF. When I follow this procedure, I never see fuel stains on the nosewheel wheelpant. One of our pilots has suggested that fuel should not drain from the engine when the auxiliary fuel pump is left on too long. He thinks there is a leak in the fuel system. Does anyone know the answer to this question? Thanks Stephen Ashley |
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wrote:
One of our pilots has suggested that fuel should not drain from the engine when the auxiliary fuel pump is left on too long. He thinks there is a leak in the fuel system. Does anyone know the answer to this question? I see this all the time on all of my local flight school C172 SPs and it is always because someone primes the engine too long. The tube is an overflow and it is working as designed when it is dumping fuel on the ground because some inexperienced pilot is not following the POH's engine start method. -- Peter ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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wrote in message ... On 16 Apr 2005 18:15:40 -0700, wrote: snip Does anyone know the answer to this question? Thanks Stephen Ashley If the pump is on, and the mixture control is NOT in ICO, there is fuel being supplied to the engine, whether the engine is running or not. Eventually, it will run down the induction system and out of the drain/drains that are in place to port it outside of the cowling (and onto the wheel fairing, apparently) TC Once the carb bowl fills, the carb float closes the valve that allows more fuel in to the carb. This prevents excess fuel from being poured into the carb and eventually leaking out. The original poster needs to check a little deeper and figure out exactly where the fuel is coming from. If it is excess fuel coming from the carb bowl, there is a problem with the carb float or the valve it controls. Perhaps the carb float has sunk, stuck, or is improperly adjusted. It is also possible that the valve no longer seats properly due to wear or some sort of obstruction. Another possiblilty is a leak in the fuel strainer valve that only manifests itself with the aux pump on... Again, there is more investigation to be done. KB |
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On Sun, 17 Apr 2005 21:05:08 -0400, "Kyle Boatright"
wrote: Once the carb bowl fills, the carb float closes the valve that allows more fuel in to the carb. This prevents excess fuel from being poured into the carb and eventually leaking out. The original poster needs to check a little deeper and figure out exactly where the fuel is coming from. If it is excess fuel coming from the carb bowl, there is a problem with the carb float or the valve it controls. Perhaps the carb float has sunk, stuck, or is improperly adjusted. It is also possible that the valve no longer seats properly due to wear or some sort of obstruction. Another possiblilty is a leak in the fuel strainer valve that only manifests itself with the aux pump on... Could be wrong, but am thinking the SP is fuel injected. Apologies in advance if it is not. TC |
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wrote in message ... On Sun, 17 Apr 2005 21:05:08 -0400, "Kyle Boatright" wrote: Once the carb bowl fills, the carb float closes the valve that allows more fuel in to the carb. This prevents excess fuel from being poured into the carb and eventually leaking out. The original poster needs to check a little deeper and figure out exactly where the fuel is coming from. If it is excess fuel coming from the carb bowl, there is a problem with the carb float or the valve it controls. Perhaps the carb float has sunk, stuck, or is improperly adjusted. It is also possible that the valve no longer seats properly due to wear or some sort of obstruction. Another possiblilty is a leak in the fuel strainer valve that only manifests itself with the aux pump on... Could be wrong, but am thinking the SP is fuel injected. Apologies in advance if it is not. TC You may just be right... KB |
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"Kyle Boatright" wrote in message ... If the pump is on, and the mixture control is NOT in ICO, there is fuel being supplied to the engine, whether the engine is running or not. Eventually, it will run down the induction system and out of the drain/drains that are in place to port it outside of the cowling (and onto the wheel fairing, apparently) TC Once the carb bowl fills, the carb float closes the valve that allows more fuel in to the carb. This prevents excess fuel from being poured into the carb and eventually leaking out. The original poster needs to check a little deeper and figure out exactly where the fuel is coming from. If it is excess fuel coming from the carb bowl, there is a problem with the carb float or the valve it controls. Perhaps the carb float has sunk, stuck, or is improperly adjusted. It is also possible that the valve no longer seats properly due to wear or some sort of obstruction. Another possiblilty is a leak in the fuel strainer valve that only manifests itself with the aux pump on... Again, there is more investigation to be done. KB The 172SP uses the IO-360-L2A which is fuel injected....i.e no carb bowl. TC is correct. If the aux pump is "on" and the mixture is not in ICO then fuel will eventually run out if the prop is stopped. J. Severyn KLVK |
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