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Lycoming Engine Fuel Flow Problem...

 
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Matt Dralle
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Joined: 08 Nov 2005
Posts: 26321
Location: Livermore CA USA
PostPosted: Tue Nov 17, 2015 7:28 pm    Post subject: Lycoming Engine Fuel Flow Problem... Reply with quote
Dear Listers,

I flew the RV-6 tonight that has a 1660 hour Lycoming O-360A1A with a Hartzell CS prop. I flew it 7 hours over a 3-day period about a week and a half ago with no issues whatsoever. Tonight, on take off, the EGT's all climbed into the 1450's right after take off and the CHT's were in the 400-450 range. The mixture was full rich. The engine didn't seem to be underpowered or rough but the fuel flow was about 9-10 GPH when it should have been in the 17-19GPH range. On the downwind I tried fiddling with the mixture with no change in making it richer. The mixture did make it leaner. I switched from the right to the left fuel tanks with no change. I have two fuel flow transducers one feeding the Skyview and the other feeding a Matronics FuelChec DX. Both were reading similarly low fuel flows at full throttle - 9-10gph. I didn't think to flip on the electric boost pump. But the flow definitely seemed restricted. The mixture control seems to have normal throw in and out and isn't binding and does lean the engine. I came in and landed with no issues.

I haven't pulled the cowling yet to have a look to see if its something obvious with the mixture cable, but what are some thoughts on what this could be?

Mechanical Fuel Pump?

Something in the Carb?

Plugged fuel line?

??

Thanks for your feedback,

Matt

-
Matt Dralle

RV-8 #82880 N998RV "Ruby Vixen"
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Status: 260+ Hours TTSN - Version 2.0 Now Flying!

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dalamphere(at)comcast.net
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PostPosted: Wed Nov 18, 2015 2:05 am    Post subject: Lycoming Engine Fuel Flow Problem... Reply with quote
Matt,

Check the carb to see if the two halves are loose. I have seen the screws that hold the two halves together get loose. Mind you,
I’m talking about 10-15 degrees loose - as the metal tabs will keep them from backing out entirely - but they can get loose to the point that the vacuum seal between the upper and lower portions of the carb is broken. When this happened to me, the mixture went lean on it’s own.
How much? - like you are at 10,000 feet and you hardly need to lean it out at cruise (2300-2400 rpm).

If you run 100LL a lot, this will also show up as blue stains on the sides of the carb.

It’s a possibility.

Dave

Quote:
On Nov 17, 2015, at 10:26 PM, Matt Dralle <dralle(at)matronics.com> wrote:




Dear Listers,

I flew the RV-6 tonight that has a 1660 hour Lycoming O-360A1A with a Hartzell CS prop. I flew it 7 hours over a 3-day period about a week and a half ago with no issues whatsoever. Tonight, on take off, the EGT's all climbed into the 1450's right after take off and the CHT's were in the 400-450 range. The mixture was full rich. The engine didn't seem to be underpowered or rough but the fuel flow was about 9-10 GPH when it should have been in the 17-19GPH range. On the downwind I tried fiddling with the mixture with no change in making it richer. The mixture did make it leaner. I switched from the right to the left fuel tanks with no change. I have two fuel flow transducers one feeding the Skyview and the other feeding a Matronics FuelChec DX. Both were reading similarly low fuel flows at full throttle - 9-10gph. I didn't think to flip on the electric boost pump. But the flow definitely seemed restricted. The mixture control seems to have normal throw in and out a!
nd isn't binding and does lean the engine. I came in and landed with no issues.

I haven't pulled the cowling yet to have a look to see if its something obvious with the mixture cable, but what are some thoughts on what this could be?

Mechanical Fuel Pump?

Something in the Carb?

Plugged fuel line?

??

Thanks for your feedback,

Matt

-
Matt Dralle

RV-8 #82880 N998RV "Ruby Vixen"
http://www.mattsrv8.com - Matt's Complete RV-8 Construction Log
http://www.mattsrv8.com/Mishap - Landing Mishap Rebuild Log
http://www.youtube.com/MattsRV8 - Matt's RV-8 HDTV YouTube Channel
Status: 260+ Hours TTSN - Version 2.0 Now Flying!

RV-6 #20916 N360EM "The Flyer"
http://www.mattsrv6.com - Matt's RV-6 Revitalization Log
Status: 350+ Hours - Full Flyer Mode!

Matt's Livermore Airport Live ATC Stream!
Check out the live ATC stream directly from my hangar at the Livermore
Airport. Includes both Tower and Ground transmissions. Archives too!
For entertainment purposes only. http://klvk.matronics.com








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jim(at)PoogieBearRanch.co
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PostPosted: Wed Nov 18, 2015 7:24 am    Post subject: Lycoming Engine Fuel Flow Problem... Reply with quote
I would check the air filter to make sure there is no blockage to the
inlet air. If it were collapsed (or "mushy") it could partially block
the air intake to the engine.

Let us know what you find...

Jim Parker
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stuart(at)stuarthutchison
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PostPosted: Wed Nov 18, 2015 3:24 pm    Post subject: Lycoming Engine Fuel Flow Problem... Reply with quote
A blocked filter would make the engine run rich, so this is more likely to be an engine fuel system blockage. Has there been any recent signs of contamination in the gascolator? How long has the carby been in service since last overhaul? Are there any signs of blue staining on the engine-driven fuel pump overflow pipe (which only vents if there is a hole in the diaphragm), which might indicate low fuel pressure (with the boost pump off).

You're approaching detonation pre-conditions, so I wouldn’t dream of getting airborne again until the fuel flows are resolved mate!

Cheers, Stu
[quote] On 19 Nov 2015, at 02:23, <jim(at)poogiebearranch.com> <jim(at)poogiebearranch.com> wrote:



I would check the air filter to make sure there is no blockage to the
inlet air. If it were collapsed (or "mushy") it could partially block
the air intake to the engine.

Let us know what you find...

Jim Parker


------

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